I did an interview a while back about what to do if you don’t like your child’s friends. You can find the article here: http://www.chicagotribune.com/lifestyles/parenting/sc-fam-dont-like-childs-friend-0911-story.html
The bottom line is, when you have a teenager, you will have to pick your battles wisely. The more you push your child into or away from something or someone, you will likely get equal or stronger pushback from them. The work of adolescence is about becoming your own person and part of that is trying on different identities. As the grown up, you may wonder who this person in your house is. Do your best to approach with curiosity instead of judgment. Ask honest questions and let your child know that you love them no matter what. That said, if they are engaging in dangerous behaviors, you will need to set clear boundaries. Nobody said it would be easy!