Or how about we actually all have to find the Avatar....The Avatar is created by the GM, who is the only one who can control when the Avatar is found. Once the GM decides that the Avatar is found. They control the Avatars actions. They decide whether he will listen to which tribe, and depending on how many people join in. The tribes can get together and try and find a way of getting the Avatar's attention. Whether it be in a Positive force. or in a negative force. The decision lies with the GM.....
Just come up with this at stupid o clock in the morning...so need sleep but it's an idea to throw in