That’s the default behavior. If you’re not getting a list of matches, open your browser console to see what’s going wrong with the AJAX request that fetches the list of matches.
Note that if you type the @ symbol, you won’t find matches, so just start typing the username or display name.
Assuming there are no errors on your site….
afaik, the auto-complete only handles friends by default. So if you aren’t friends with ‘Jenn’, you won’t see a suggestion.
To turn on auto-complete for all users, put this in bp-custom.php :
define( 'BP_MESSAGES_AUTOCOMPLETE_ALL', true );
Thanks so much! I believe these were both helpful hints.