The Cannonballs are castaways located on Cannonball Run. They can be found after discovering their message in a bottle and using the treasure map within the bottle.
The message in a bottle to locate these castaways was last visible 2 days ago on 4 July. It will be visible again in 4 days on 10 July. (wrong?) Once a message in a bottle is found and when a player has walked near its spawn location when it was visible it will always be visible, unless the message in the bottle or its treasure map is in the player's bank or inventory.
They are a group of cannibals who misidentify themselves as Cannonballs due to a speech impediment. They are Jellyhead-head, Cannonballhead, Puddinghead and Fishmaskhead.