Good work removing her internet etc.
Dont' beat yourself up, and this must be so scary for you. Your daughter is way past discipline being an effective way to get her to make the right choices, not that you shouldn't use it, but be sure from now on your tone and message when enforcing rules is logical, calm and loving and "because she's almost an adult, and you understand her needs and desires".Sort of like, "I understand boys are exciting, and that you're feeling lonely and bored, and you're a mature and special girl, and want to meet new people and feel accepted, but because of the danger involved, and the fact that for just a couple more short years, your are my responsibility and I am supporting you, I can't allow you to put yourself at risk like that. If you choose to do dangerous things, I have to remove the possibility for you as much as I can." I agree with the post below to gather the news stories to back up your position.
On a separate note, at other times not having to do with discipline, you REALLY need to keep this girl busy, and broaden her horizons. Bored kids tend to look for excitement. What are her interests? She needs to prepare for life and college soon. Are there classes/activities in addition to skating she can be doing outside of school to build a special resume for herself and meet driven responsible friends? Sounds like her skating isn't taking up enough of her spare time, even though that's definitely great. She needs close bonds and activities WITH good people. Even church groups do fun things, charity missions etc, and her peers would be nicer than older boys with drugs.
And most of all, I was working my buns off at that age bagging groceries and babysitting and washing dishes in a local restaurant to pay for all my extra privileges and leisure time (of which I had almost none, but I bought my own wild fashions and movie tickets and albums etc). She shouldn't have time for these hook ups and seeking excitement. She should be sleeping when she's not in school, doing homework, skating, socializing with good people, or being productive.
If you can possibly swing it, you and she should travel somewhere new together to give her a new perspective and allow for some long talks on buses/planes. Start to look for ways to enrich her perspective and keep her distracted from this wrong path. And also be sure to have all the thorough sex and disease talks-but in a way that shows you know she's mature, and you too were not born yesterday and her generation didn't invent sex.
Good, luck, hang in there. I think the counseling could be OK, but didn't do me much good as a troubled teen. It was my busy schedule that really kept me from getting in too much trouble. That and the fact that I had my sights on higher things I had glimpsed traveling (military dad). I didn't want to be trapped in a "boring life" and that kept me somewhat driven. And thank god there was no internet then. We had to meet trouble makers out and about, but there was no way for them to reach us at home other than to call the landline and probably get a parent answering!!!! (lots of hang ups in the teen years)
Good luck momma-thanks for the wake up call to us all-mine are younger...eeek.