I have personally talked to prostitutes who were groomed into it while being sexually abused as young teens. (13 in one case - given what she thought was cannabis resin by a "boyfriend", but in fact turned out to be heroin, in order to get her dependent on drugs and desperate, then pimped out by the boyfriend. One of the many tragic things about her story was she felt guilty about her past, as if she was responsible for having been abused as a child.)
I have a friend who works in public health, and liaises with our local police. Trafficking in the sense of moving underage girls away from their families to the next town to work in brothels is endemic in our (fairly rural) county.