diff --git a/lib/selectors/user-selectors.js b/lib/selectors/user-selectors.js
--- a/lib/selectors/user-selectors.js
+++ b/lib/selectors/user-selectors.js
@@ -113,36 +113,38 @@
   baseRelativeMemberInfoSelectorForMembersOfThread,
 );
 
+function filterPotentialMembers(
+  userInfos: UserInfos,
+  currentUserID: ?string,
+): { [id: string]: AccountUserInfo } {
+  const availableUsers: { [id: string]: AccountUserInfo } = {};
+
+  for (const id in userInfos) {
+    const { username, relationshipStatus } = userInfos[id];
+    if (id === currentUserID || !username) {
+      continue;
+    }
+    if (
+      relationshipStatus !== userRelationshipStatus.BLOCKED_VIEWER &&
+      relationshipStatus !== userRelationshipStatus.BOTH_BLOCKED
+    ) {
+      availableUsers[id] = { id, username, relationshipStatus };
+    }
+  }
+  return availableUsers;
+}
+
 const userInfoSelectorForPotentialMembers: (state: BaseAppState<*>) => {
   [id: string]: AccountUserInfo,
 } = createSelector(
   (state: BaseAppState<*>) => state.userStore.userInfos,
   (state: BaseAppState<*>) => state.currentUserInfo && state.currentUserInfo.id,
-  (
-    userInfos: UserInfos,
-    currentUserID: ?string,
-  ): { [id: string]: AccountUserInfo } => {
-    const availableUsers: { [id: string]: AccountUserInfo } = {};
-
-    for (const id in userInfos) {
-      const { username, relationshipStatus } = userInfos[id];
-      if (id === currentUserID || !username) {
-        continue;
-      }
-      if (
-        relationshipStatus !== userRelationshipStatus.BLOCKED_VIEWER &&
-        relationshipStatus !== userRelationshipStatus.BOTH_BLOCKED
-      ) {
-        availableUsers[id] = { id, username, relationshipStatus };
-      }
-    }
-    return availableUsers;
-  },
+  filterPotentialMembers,
 );
 
 function searchIndexFromUserInfos(userInfos: {
   [id: string]: AccountUserInfo,
-}) {
+}): SearchIndex {
   const searchIndex = new SearchIndex();
   for (const id in userInfos) {
     searchIndex.addEntry(id, userInfos[id].username);
@@ -214,4 +216,6 @@
   isLoggedIn,
   userStoreSearchIndex,
   usersWithPersonalThreadSelector,
+  filterPotentialMembers,
+  searchIndexFromUserInfos,
 };
diff --git a/lib/shared/search-utils.js b/lib/shared/search-utils.js
--- a/lib/shared/search-utils.js
+++ b/lib/shared/search-utils.js
@@ -21,12 +21,16 @@
 function getPotentialMemberItems(
   text: string,
   userInfos: { +[id: string]: AccountUserInfo },
-  searchIndex: SearchIndex,
+  inputSearchIndex: SearchIndex | $ReadOnlyArray<SearchIndex>,
   excludeUserIDs: $ReadOnlyArray<string>,
   inputParentThreadInfo: ?ThreadInfo,
   inputCommunityThreadInfo: ?ThreadInfo,
   threadType: ?ThreadType,
 ): UserListItem[] {
+  const searchIndexes = Array.isArray(inputSearchIndex)
+    ? inputSearchIndex
+    : [inputSearchIndex];
+
   const communityThreadInfo =
     inputCommunityThreadInfo && inputCommunityThreadInfo.id !== genesis.id
       ? inputCommunityThreadInfo
@@ -74,9 +78,11 @@
       appendUserInfo(userInfos[id]);
     }
   } else {
-    const ids = searchIndex.getSearchResults(text);
-    for (const id of ids) {
-      appendUserInfo(userInfos[id]);
+    for (const searchIndex of searchIndexes) {
+      const ids = searchIndex.getSearchResults(text);
+      for (const id of ids) {
+        appendUserInfo(userInfos[id]);
+      }
     }
   }
 
diff --git a/web/chat/chat-message-list-container.react.js b/web/chat/chat-message-list-container.react.js
--- a/web/chat/chat-message-list-container.react.js
+++ b/web/chat/chat-message-list-container.react.js
@@ -18,7 +18,6 @@
   threadIsPending,
 } from 'lib/shared/thread-utils.js';
 import { threadTypes } from 'lib/types/thread-types.js';
-import type { AccountUserInfo } from 'lib/types/user-types.js';
 
 import ChatInputBar from './chat-input-bar.react.js';
 import css from './chat-message-list-container.css';
@@ -38,13 +37,20 @@
   const isChatCreation =
     useSelector(state => state.navInfo.chatMode) === 'create';
 
-  const selectedUserIDs = useSelector(state => state.navInfo.selectedUserList);
+  const selectedUserIDs = useSelector(
+    state => state.navInfo.selectedUserList ?? [],
+  );
   const otherUserInfos = useSelector(userInfoSelectorForPotentialMembers);
-  const userInfoInputArray: $ReadOnlyArray<AccountUserInfo> = React.useMemo(
-    () => selectedUserIDs?.map(id => otherUserInfos[id]).filter(Boolean) ?? [],
-    [otherUserInfos, selectedUserIDs],
+  const [userInfoInputArray, setUserInfoInputArray] = React.useState(() =>
+    selectedUserIDs.map(id => otherUserInfos[id]).filter(Boolean),
   );
 
+  React.useEffect(() => {
+    if (!isChatCreation) {
+      setUserInfoInputArray([]);
+    }
+  }, [isChatCreation]);
+
   const loggedInUserInfo = useLoggedInUserInfo();
   invariant(loggedInUserInfo, 'loggedInUserInfo should be set');
 
@@ -110,52 +116,46 @@
   invariant(threadInfo, 'ThreadInfo should be set');
 
   const dispatch = useDispatch();
-
-  // The effect removes members from list in navInfo
-  // if some of the user IDs don't exist in redux store
   React.useEffect(() => {
-    if (!isChatCreation) {
-      return;
-    }
-    const existingSelectedUsersSet = new Set(
-      userInfoInputArray.map(userInfo => userInfo.id),
-    );
-    if (
-      selectedUserIDs?.length !== existingSelectedUsersSet.size ||
-      !_isEqual(new Set(selectedUserIDs), existingSelectedUsersSet)
-    ) {
-      dispatch({
-        type: updateNavInfoActionType,
-        payload: {
-          selectedUserList: Array.from(existingSelectedUsersSet),
-        },
-      });
-    }
-  }, [
-    dispatch,
-    isChatCreation,
-    otherUserInfos,
-    selectedUserIDs,
-    userInfoInputArray,
-  ]);
+    if (isChatCreation) {
+      let payload = null;
 
-  React.useEffect(() => {
-    if (isChatCreation && activeChatThreadID !== threadInfo?.id) {
-      let payload = {
-        activeChatThreadID: threadInfo?.id,
-      };
-      if (threadIsPending(threadInfo?.id)) {
+      const newSelectedUserIDs = userInfoInputArray.map(user => user.id);
+      if (!_isEqual(new Set(selectedUserIDs), new Set(newSelectedUserIDs))) {
+        payload = {
+          ...payload,
+          selectedUserList: newSelectedUserIDs,
+        };
+      }
+
+      if (activeChatThreadID !== threadInfo?.id) {
         payload = {
           ...payload,
-          pendingThread: threadInfo,
+          activeChatThreadID: threadInfo?.id,
         };
+        if (threadIsPending(threadInfo?.id)) {
+          payload = {
+            ...payload,
+            pendingThread: threadInfo,
+          };
+        }
+      }
+      if (!payload) {
+        return;
       }
       dispatch({
         type: updateNavInfoActionType,
         payload,
       });
     }
-  }, [activeChatThreadID, dispatch, isChatCreation, threadInfo]);
+  }, [
+    activeChatThreadID,
+    dispatch,
+    isChatCreation,
+    selectedUserIDs,
+    threadInfo,
+    userInfoInputArray,
+  ]);
 
   const inputState = React.useContext(InputStateContext);
   invariant(inputState, 'InputState should be set');
@@ -230,6 +230,7 @@
     const chatUserSelection = (
       <ChatThreadComposer
         userInfoInputArray={userInfoInputArray}
+        setUserInfoInputArray={setUserInfoInputArray}
         otherUserInfos={otherUserInfos}
         threadID={threadInfo.id}
         inputState={inputState}
diff --git a/web/chat/chat-thread-composer.react.js b/web/chat/chat-thread-composer.react.js
--- a/web/chat/chat-thread-composer.react.js
+++ b/web/chat/chat-thread-composer.react.js
@@ -3,12 +3,23 @@
 import * as React from 'react';
 import { useDispatch } from 'react-redux';
 
+import { searchUsers } from 'lib/actions/user-actions.js';
 import SWMansionIcon from 'lib/components/SWMansionIcon.react.js';
 import { useENSNames } from 'lib/hooks/ens-cache.js';
-import { userSearchIndexForPotentialMembers } from 'lib/selectors/user-selectors.js';
+import {
+  filterPotentialMembers,
+  userSearchIndexForPotentialMembers,
+  searchIndexFromUserInfos,
+} from 'lib/selectors/user-selectors.js';
 import { getPotentialMemberItems } from 'lib/shared/search-utils.js';
 import { threadIsPending } from 'lib/shared/thread-utils.js';
-import type { AccountUserInfo, UserListItem } from 'lib/types/user-types.js';
+import type { SetState } from 'lib/types/hook-types.js';
+import type {
+  AccountUserInfo,
+  UserListItem,
+  GlobalAccountUserInfo,
+} from 'lib/types/user-types.js';
+import { useServerCall } from 'lib/utils/action-utils.js';
 
 import css from './chat-thread-composer.css';
 import Button from '../components/button.react.js';
@@ -20,6 +31,7 @@
 
 type Props = {
   +userInfoInputArray: $ReadOnlyArray<AccountUserInfo>,
+  +setUserInfoInputArray: SetState<$ReadOnlyArray<AccountUserInfo>>,
   +otherUserInfos: { [id: string]: AccountUserInfo },
   +threadID: string,
   +inputState: InputState,
@@ -30,12 +42,55 @@
   | 'keep-active-thread';
 
 function ChatThreadComposer(props: Props): React.Node {
-  const { userInfoInputArray, otherUserInfos, threadID, inputState } = props;
+  const {
+    userInfoInputArray,
+    setUserInfoInputArray,
+    otherUserInfos,
+    threadID,
+    inputState,
+  } = props;
 
   const [usernameInputText, setUsernameInputText] = React.useState('');
 
-  const dispatch = useDispatch();
+  const userInfos = useSelector(state => state.userStore.userInfos);
+  const viewerID = useSelector(state => state.currentUserInfo?.id);
+
+  const [serverSearchUserInfos, setServerSearchUserInfos] = React.useState<
+    $ReadOnlyArray<GlobalAccountUserInfo>,
+  >([]);
+  const callSearchUsers = useServerCall(searchUsers);
+  React.useEffect(() => {
+    (async () => {
+      if (usernameInputText.length === 0) {
+        setServerSearchUserInfos([]);
+      } else {
+        const { userInfos: serverUserInfos } = await callSearchUsers(
+          usernameInputText,
+        );
+        setServerSearchUserInfos(serverUserInfos);
+      }
+    })();
+  }, [callSearchUsers, usernameInputText]);
+
+  const filteredServerUserInfos = React.useMemo(() => {
+    const result = {};
+    for (const user of serverSearchUserInfos) {
+      if (!(user.id in userInfos)) {
+        result[user.id] = user;
+      }
+    }
+    return filterPotentialMembers(result, viewerID);
+  }, [serverSearchUserInfos, userInfos, viewerID]);
+
+  const mergedUserInfos = React.useMemo(
+    () => ({ ...filteredServerUserInfos, ...otherUserInfos }),
+    [filteredServerUserInfos, otherUserInfos],
+  );
+
   const userSearchIndex = useSelector(userSearchIndexForPotentialMembers);
+  const filteredServerUsersSearchIndex = React.useMemo(() => {
+    return searchIndexFromUserInfos(filteredServerUserInfos);
+  }, [filteredServerUserInfos]);
 
   const userInfoInputIDs = React.useMemo(
     () => userInfoInputArray.map(userInfo => userInfo.id),
@@ -46,42 +101,38 @@
     () =>
       getPotentialMemberItems(
         usernameInputText,
-        otherUserInfos,
-        userSearchIndex,
+        mergedUserInfos,
+        [userSearchIndex, filteredServerUsersSearchIndex],
         userInfoInputIDs,
       ),
-    [usernameInputText, otherUserInfos, userSearchIndex, userInfoInputIDs],
+    [
+      usernameInputText,
+      mergedUserInfos,
+      userSearchIndex,
+      filteredServerUsersSearchIndex,
+      userInfoInputIDs,
+    ],
   );
   const userListItemsWithENSNames = useENSNames(userListItems);
 
   const onSelectUserFromSearch = React.useCallback(
-    (id: string) => {
-      const selectedUserIDs = userInfoInputArray.map(user => user.id);
-      dispatch({
-        type: updateNavInfoActionType,
-        payload: {
-          selectedUserList: [...selectedUserIDs, id],
-        },
-      });
+    (id: string, username: string) => {
+      setUserInfoInputArray(previousUserInfoInputArray => [
+        ...previousUserInfoInputArray,
+        { id, username },
+      ]);
       setUsernameInputText('');
     },
-    [dispatch, userInfoInputArray],
+    [setUserInfoInputArray],
   );
 
   const onRemoveUserFromSelected = React.useCallback(
     (id: string) => {
-      const selectedUserIDs = userInfoInputArray.map(user => user.id);
-      if (!selectedUserIDs.includes(id)) {
-        return;
-      }
-      dispatch({
-        type: updateNavInfoActionType,
-        payload: {
-          selectedUserList: selectedUserIDs.filter(userID => userID !== id),
-        },
-      });
+      setUserInfoInputArray(previousUserInfoInputArray =>
+        previousUserInfoInputArray.filter(user => user.id !== id),
+      );
     },
-    [dispatch, userInfoInputArray],
+    [setUserInfoInputArray],
   );
 
   const userSearchResultList = React.useMemo(() => {
@@ -98,7 +149,12 @@
           <li key={userSearchResult.id} className={css.searchResultsItem}>
             <Button
               variant="text"
-              onClick={() => onSelectUserFromSearch(userSearchResult.id)}
+              onClick={() =>
+                onSelectUserFromSearch(
+                  userSearchResult.id,
+                  userSearchResult.username,
+                )
+              }
               className={css.searchResultsButton}
             >
               <div className={css.userName}>{userSearchResult.username}</div>
@@ -115,6 +171,7 @@
     usernameInputText,
   ]);
 
+  const dispatch = useDispatch();
   const hideSearch = React.useCallback(
     (threadBehavior: ActiveThreadBehavior = 'keep-active-thread') => {
       dispatch({