You should a plugin which will allow players to add others as a friend within the server by using the command /friend add (username). When a friend joins there server it could come up in the chat feed “Your friend PizzaFella is online.” you could also make a friend group chat as a feature so you can all talk together instead of talking in public chat and making it crowded for over players (/friend groupchat create StevesFriends) and the to join / leave the chat you could have /friends chat StevesFriends which will then enable the groupchat
That is basicly what a gang does