I have a hard time finding Groups or getting people to stay in group while we find more members

I downloaded this game for the co-op play. But I been finding it hard to play with other players because of the group finder and matchmaking. there arent many Public Groups in the menu, and when you do make a group, people wont stay as you try to build a full party.
Would hope the developers come up with a solution to this and improve the methods for players to play with other players in the game.