Since You've Been Gone (9781459728189) by Mary Jennifer Payne

On the run from her abusive father, fifteen-year-old Edie Fraser and her mother flee to London, England for a fresh start. But one day, Edie's mom doesn't come home from work. Afraid to phone the police and risk being returned to her father, Edie begins a desperate search for her mother, and finds an unlikely ally along the way.