The goblins steal goo, but the key is to unleash them in towns that aren't checked upon all the time because if the person squishes the goblins before the collect goo, then you don't get any.
Usually when I start up the app, the goblins will have collected between 75-100 goo viles.
Do you have to wait for the GOO and monies to be added to your total before you leave for a different friend or does it automatically add to it when you leave?