Recieve Notification when a friend starts a ride, like Zwift. Show them on a map. Try to meetup.
I would implement a feature similar to Zwift where it notifies you when a starred friend starts a ride. This way you can more spontaneously chose to go meet up with them, give them a thumbs up, or feel motivated to get out and ride too. I am on a team where many of us live across the city. We ride alone a lot on days where meetups are difficult to arrange, but that doesn't mean we couldn't plan to chase after another rider or meet up somewhere along their route.
It would be interesting if the feature would show you their pre-selected route if they have one, if not where they currently are so I can text them or call them to try and meet them.