The best thing you can do is tell someone who can help him. A teacher, a parent, someone of authority. He may get mad at you for a while, but you might save his life by doing so. I know this from experience. If he's cutting now, you have no idea what could happen in the future. Talk to him, let him know you really care, keep bringing it up to him, find out what is making him want to do it and just be a friend.
Nothing. If you try to change him, he'll only resent you. For many people who cut themselves, their cutting is a form of stress relief. It may very well be the only thing that keeps him from killing himself.
I wasn't aware only "emo"people cut themselves.I used to go out with a girl that had scars all up her shoulder from doing that .She was just a lunatic...not emo.I tried to help her and tried to understand why she did it...but she just wasted 2 years of my life.Try to help your friend,but don't surprised if they don't want it.Good luck.