Google Play Games Services 2017: How to invite somebody to a multiplayer match?

Google announced in December 2016 that Google+ is no longer integrated in Google Play Games Services: https://android-developers.googleblog.com/2016/12/games-authentication-adopting-google.html And as a result, a call of Unities Social.localUser.LoadFriends() method returns zero friends. Now with no friends available, how do you invite other players to a multiplayer match using Googles Play Games Services?