My friend is cutting and I don't know what to do.?

I have this one friend and she is cutting, she cuts in class all the time and somehow the teachers don't see her. Me and my friends want to tell someone but none of us know who to tell, plus my friend would get mad if we told on her. And today at school she asked me and some of our friends to take her scissors, she only gave us the three pairs she had with her, and she is bringing the other pairs tomorrow, she also wanted to know if we were going to take away her safety pins and thumb tacks and her pocket knife, and we said yes. Plus lately I have been thinking about cutting as well, I have never cut before and I don't know if I should. I don't know how to stop my friend from cutting either. What should I do, I mean I'm really confused on this and I don't really know who I can talk to about this stuff besides my friends, but if I told my friends I was thinking about cutting they would get mad and tell me I can't and that if I did they would take all my scissors and blades, I just don't know what to do.