Please tell me what to do...

First, 你 have to make it clear to your colleague that he is not alone, that there is a lot 更多 people going through that situation (me too) and that the only way to solve this problem and telling their parents and teachers to they can talk to the bullies and maybe even transfer them to school.
tries to get your colleague to integrate in your group of friends, family, 你 feel good when the foot of 你 and tell 你 that alcohol and the fact that 你 feel intimidated only worsens the situation, if 你 all ye a group of 老友记 (true) attached, will be much 更多 difficult bullies are teasing you, because they only like to mess with guys weaker 或者 更多 isolated problems, 加入 你 all and help your friend, hence the the thugs who do not understand 你 feel intimidated and speak with teachers and staff from our school to remain alert.
together to get 你 going stop them!

if 你 need 更多 clarification do 你 doubt, 你 know I'm here to help you.

(SORRY THE BAD ENGLISH)

Just stand up for him. Don't care what other people think of him because thats not your business for 你 to know what they think of him. But if it is getting out of control, tell someone 你 trust like a parent, a teacher 或者 a friend and he will get the help he needs.