Search and Add Users to Instant Messages Friend List
Click the Message Alerts icon at the top of the page.
Click Instant Messages.
A pop-up window will open. Click Friends, then Click Add Friends and select Search Users. Note: Add by Username is an option but not recommended, as it requires you to have the exact username for the user.
Type the user you wish to add in the search field, then hit enter/return on your keyboard to search. The search results will display.
Check the box next to the user you wish to add, then click Add as Friend.