Pinning, muting, blocking, and archiving all live in each chat’s Conversation Settings panel; message search sits behind the magnifying glass in the chat header.
Open the chat, click the Options menu (three dots) in the header and choose Conversation Settings, or right-click the chat in the sidebar. Changes apply as you make them; there is nothing to save.
Note: Account-wide preferences (notifications, privacy, appearance) live under Chat Settings in the same menu’s All chats group.
Pin a chat
Right-click a chat in the sidebar (press and hold on a phone) and choose Pin, or use the Pin to top switch in Conversation Settings. Pinned chats move to a row of circles at the top of the sidebar; right-click a circle to Unpin.
Mute a chat
In Conversation Settings, choose from the Mute this conversation list: 8 hours, 24 hours, 1 week, or until you turn it back on. A timed mute lifts itself when the time is up, and the panel tells you when that is. Set it back to Notifications on to unmute early. For a quick mute with no end date, right-click the chat in the sidebar and choose Mute.
Muting silences the sound and desktop pop-up for that conversation, but you still see the unread badge. A bell-with-a-line icon marks muted chats in the sidebar. To silence every conversation at once, turn on Mute All Chats under All Chat Settings → Notifications.
Block someone
Blocking lives in Conversation Settings → Privacy & Safety and stops messages in both directions: see How do I block someone in Messages?.
Archive a chat
Right-click the chat and choose Archive chat (or use Archive in Conversation Settings) to move it out of your main list. Archiving only hides the thread from your own list; in a group chat you stay a member, unlike leaving. A new message unarchives the chat automatically.
Click the Archived tab at the top of the chat sidebar to see archived chats; right-click one and choose Unarchive to move it back.
Search messages
Open a conversation and click the magnifying glass in the chat header. Type at least two characters and results appear as you type. Click a result and the conversation scrolls straight to that message, highlighted.
A Jump to latest button brings you back to the newest messages; sending a message does the same.
Note: You can also pin individual messages and view all pinned messages from the chat header.