My 15 year old brother is being bullied and hared at school...?

My brother and i go to the same high school well lately my brother has been getting bullied and hared and i don't understand why he is always hit on by all the girls in the school and he is on the track and swim team so it isn't like he is fat or anything. But it piss's me off so bad that people are doing this to him and i feel like punching them at times. And whenever he retaliates he is the only one to get into trouble and he has told the teachers and principles but nothing gets done. Is there something i can do? He is so scared of telling our parents, advice?