You get to open chests on people's Island that contain coins. The Icon on the left tells you how many you have left to open....you can visit 5 friends and open 5 chests on each. The icon counts down to zero.
I've Also lost my friends and I have found myself in a brand new game when I was doing so well before and starting all over again. No one to play with, no friends island to visit. Getting lonesome here on the island.