diff --git a/keyserver/src/creators/message-report-creator.js b/keyserver/src/creators/message-report-creator.js
new file mode 100644
--- /dev/null
+++ b/keyserver/src/creators/message-report-creator.js
@@ -0,0 +1,141 @@
+// @flow
+
+import bots from 'lib/facts/bots';
+import { createMessageReply } from 'lib/shared/message-utils';
+import { type MessageReportCreationRequest } from 'lib/types/message-report-types';
+import { messageTypes } from 'lib/types/message-types';
+import type { RawMessageInfo } from 'lib/types/message-types';
+import type { ServerThreadInfo } from 'lib/types/thread-types';
+import { ServerError } from 'lib/utils/errors';
+import { promiseAll } from 'lib/utils/promises';
+
+import { createCommbotThread } from '../bots/commbot';
+import { fetchMessageInfoByID } from '../fetchers/message-fetchers';
+import {
+  fetchPersonalThreadID,
+  serverThreadInfoFromMessageInfo,
+} from '../fetchers/thread-fetchers';
+import {
+  fetchUsername,
+  fetchKeyserverAdminID,
+} from '../fetchers/user-fetchers';
+import type { Viewer } from '../session/viewer';
+import createMessages from './message-creator';
+
+const { commbot } = bots;
+
+type MessageReportData = {
+  +reportedMessageText: ?string,
+  +reporterUsername: ?string,
+  +commbotThreadID: string,
+  +reportedThread: ?ServerThreadInfo,
+  +reportedMessageAuthor: ?string,
+};
+
+async function createMessageReport(
+  viewer: Viewer,
+  request: MessageReportCreationRequest,
+): Promise<RawMessageInfo[]> {
+  const {
+    reportedMessageText,
+    reporterUsername,
+    commbotThreadID,
+    reportedThread,
+    reportedMessageAuthor,
+  } = await fetchMessageReportData(viewer, request);
+
+  const reportMessage = getCommbotMessage(
+    reporterUsername,
+    reportedMessageAuthor,
+    reportedThread?.name,
+    reportedMessageText,
+  );
+  const time = Date.now();
+  const result = await createMessages(viewer, [
+    {
+      type: messageTypes.TEXT,
+      threadID: commbotThreadID,
+      creatorID: commbot.userID,
+      time,
+      text: reportMessage,
+    },
+  ]);
+  if (result.length === 0) {
+    throw new ServerError('message_report_failed');
+  }
+  return result;
+}
+
+async function fetchMessageReportData(
+  viewer: Viewer,
+  request: MessageReportCreationRequest,
+): Promise<MessageReportData> {
+  const keyserverAdminIDPromise = fetchKeyserverAdminID();
+  const reportedMessagePromise = fetchMessageInfoByID(
+    viewer,
+    request.messageID,
+  );
+  const promises = {};
+
+  promises.viewerUsername = fetchUsername(viewer.id);
+
+  const keyserverAdminID = await keyserverAdminIDPromise;
+  if (!keyserverAdminID) {
+    throw new ServerError('keyserver_admin_not_found');
+  }
+  promises.commbotThreadID = getCommbotThreadID(keyserverAdminID);
+
+  const reportedMessage = await reportedMessagePromise;
+
+  if (reportedMessage) {
+    promises.reportedThread = serverThreadInfoFromMessageInfo(reportedMessage);
+  }
+
+  const reportedMessageAuthorID = reportedMessage?.creatorID;
+  if (reportedMessageAuthorID) {
+    promises.reportedMessageAuthor = fetchUsername(reportedMessageAuthorID);
+  }
+
+  const reportedMessageText =
+    reportedMessage?.type === 0 ? reportedMessage.text : null;
+
+  const {
+    viewerUsername,
+    commbotThreadID,
+    reportedThread,
+    reportedMessageAuthor,
+  } = await promiseAll(promises);
+
+  return {
+    reportedMessageText,
+    reporterUsername: viewerUsername,
+    commbotThreadID,
+    reportedThread,
+    reportedMessageAuthor,
+  };
+}
+
+async function getCommbotThreadID(userID: string): Promise<string> {
+  const commbotThreadID = await fetchPersonalThreadID(userID, commbot.userID);
+  return commbotThreadID ?? createCommbotThread(userID);
+}
+
+function getCommbotMessage(
+  reporterUsername: ?string,
+  messageAuthorUsername: ?string,
+  threadName: ?string,
+  message: ?string,
+): string {
+  reporterUsername = reporterUsername ?? '[null]';
+  const messageAuthor = messageAuthorUsername
+    ? `${messageAuthorUsername}’s`
+    : 'this';
+  const thread = threadName ? `chat titled "${threadName}"` : 'chat';
+  const reply = message ? createMessageReply(message) : 'non-text message';
+  return (
+    `${reporterUsername} reported ${messageAuthor} message in ${thread}\n` +
+    reply
+  );
+}
+
+export default createMessageReport;
diff --git a/keyserver/src/fetchers/thread-fetchers.js b/keyserver/src/fetchers/thread-fetchers.js
--- a/keyserver/src/fetchers/thread-fetchers.js
+++ b/keyserver/src/fetchers/thread-fetchers.js
@@ -7,6 +7,7 @@
   getCommunity,
 } from 'lib/shared/thread-utils';
 import { hasMinCodeVersion } from 'lib/shared/version-utils';
+import type { RawMessageInfo, MessageInfo } from 'lib/types/message-types';
 import {
   threadTypes,
   type ThreadType,
@@ -240,6 +241,14 @@
   return threads[0]?.id.toString();
 }
 
+async function serverThreadInfoFromMessageInfo(
+  message: RawMessageInfo | MessageInfo,
+): Promise<?ServerThreadInfo> {
+  const threadID = message.threadID;
+  const threads = await fetchServerThreadInfos(SQL`t.id = ${threadID}`);
+  return threads.threadInfos[threadID];
+}
+
 export {
   fetchServerThreadInfos,
   fetchThreadInfos,
@@ -249,4 +258,5 @@
   determineThreadAncestry,
   personalThreadQuery,
   fetchPersonalThreadID,
+  serverThreadInfoFromMessageInfo,
 };
diff --git a/lib/types/message-report-types.js b/lib/types/message-report-types.js
new file mode 100644
--- /dev/null
+++ b/lib/types/message-report-types.js
@@ -0,0 +1,11 @@
+// @flow
+
+import type { RawMessageInfo } from './message-types';
+
+export type MessageReportCreationRequest = {
+  +messageID: string,
+};
+
+export type MessageReportCreationResult = {
+  +messageInfo: RawMessageInfo,
+};