Hi OP.
I was your daughter.
There honestly wasn't anything going on, I wasn't in a bad place, I wasn't unhappy. Came from a healthy, happy home.
I wasn't exploited, or groomed, or slept with anyone I didn't want to.
I went missing for weeks at a time, stayed out all night, snuck out of the house when grounded to go to parties etc etc.
I'm not even sure why I was like it tbh, I think I just wanted to be a grown up, and at the time I saw that as doing what I wanted when I wanted.
And obviously, knowing I was gonna get in the shit anyway, I would think "well I'll be in the shit anyway, may as well go that rave/ crash at mates/ stay out all night"
Not sure if you want to hear this, but I was really into raves and drugs and sex, and just wanted to do all that, all the time.
It wasn't because I was unhappy......I just really liked the lifestyle!
My DM is a social worker, she is, and was, brilliant and lovely, but like you was at the end of her tether.
It's not a reflection on you or your parenting, trust me on this.
And I will be 100% honest, I never really stopped, just got older, left home at 18, and carried on living that sort of lifestyle for a very long time.
However I got good GCSE results, got, and kept, some very good jobs, and am now a (mainly) sensible SAHM!
I don't have any answers, but I hope I can reassure you that it's not always because the kid is acting out because of deeper issues, some people just like living like that.
Good luck OP 
I know it's hard, but she will get there in the end!