The “Compose” page has a field labeled “Send To” that, when I type inside, seems to attempt to auto-fill names, but nothing happens. I checked for JavaScript errors and there were none. I have “Friend Connections” disabled, but I also tried with it enabled and the profiles being friends.
I’ve also tested for theme/plugin conflicts by deactivating all plugins except BuddyPress and activating a WP default theme. No Javascript or PHP errors are displayed.
I didn’t test it right initially. The auto-fill only works when members are friends, and when I tested it I tested it with “@username” which didn’t work.