Scared for my daughter.?

Recently I found out that my 17yr old daughter has been acting out in some rather risky behaviors. I feel like I am questioning myself about everything concerning this, her consequences, the reasons behind her doing this, and being scared she will continue down this path. While I understand she is at a age of curiosity and exploration, she truly is putting herself in harms way, taking explicit photos and posting them to her friends, getting more involved with drugs. I know many teenagers act out with drugs and alcohol because they want to fit in and seem cool, however most the time she is using pills, (etc.) she is alone. That really scares me. Does anyone have any ideas or input on how I should handle this?