There were groups in my high school days too. Some are related to activities like sports, others based on looks or race which are only used for cruelty and bullying. If you are a leader, encourage individual nick-names (apodos?) for each person but ask if they would feel bad having (x) for a nick-name.
I have seen this work as a way to keep kids individual without creating groups that become gangs, and even make war against each other. Where did I see it? In a very rough public school. Someone I mentor attends there and is a respected leader. The choice of his peers.