Button friends
The Friends List in the lower-right displays all of your friends and friended Trademasters in Paradise Bay. You can tap any friend in your list to visit their island, where you can collect karma and assist with Plongée.

Friends are the players you’ve added via Game Center or Google Play as well as friends on Facebook. There’s no limit to the number of friends you can add through these services.

Friended Trademasters are players you've added by visiting their islands via the World Market (as of Update 1.3). You can add up to 8 Trademasters using this system.


The above is Quoted in part or full directly from the Official Paradise Bay FAQ