I have been through hell and back with my DD now 16 in the past year. Going missing, sometimes for days on end; playing truant; stealing; swearing you name it.
It was fucking awful and I felt like packing a bag and going missing myself. It made life at home horrendous, and affected every aspect of our lives.
Eventually she point blank refused to go to school and I managed to get her into a College scheme. She has new friends and is back to her self. She's in on time, treats us all with respect as she should. Yes she won't have all the expected GCSEs etc but she's safe, well and happy.
What I'm trying to say is, I totally feel your pain. It's awful. I don't have any answers, other than keep doing what you're doing. It won't last forever.
If the SS are saying she's at risk of exploitation, what are they doing to help?
Ask for a family intervention worker, we had one for a few weeks and she was a good listener and support for me.
It feels really lonely, but you're not alone in this.