Which friends appear in the chat sidebar? Can I add specific friends?
The friends that show up at the top section of chat are people you’ve interacted with frequently or recently on Facebook. You can't add friends to this part, though it updates dynamically as the people you interact with change.
Scroll down your sidebar to see the rest of your friends who are on chat. To find someone quickly, you can search for them by entering their name into the search field at the bottom of your sidebar.