One of the biggest problems with human trafficking like this is people usually pick up people who won't be missed. Or, people that if they disappear won't be a big deal.
I work for a state agency and we had a guest presentation from someone who works these types of trafficking cases for our state (Texas, we got a lot of them). Specifically she was telling us about how to spot victims of trafficking in a health care setting, but had lots of really sad example. She had a case of a teenage girl who was in and out of school, she skipped class all the time to go smoke pot, she stayed out late or sometimes didn't come home...anyway all this is to say she skipped school one day and got picked off the street, held hostage in a trash house and raped for a week straight. Not just the home owners, other men came and paid to have sex with her, after a week they let her go. There wasn't even a police report filed for her absence. The school didn't think she was missing, her parents were absent/didn't care/didn't notice. Her friends thought she had just gone off/skipped down like she always said she would...a child nobody would miss. And this wasn't some random country off the grid, this was in the middle of a big city in Texas. That's the really sad truth about these cases. Either they don't have anyone to miss them, or they are presumed to be runaways/aren't thought to be in immediate danger. The whole "Taken" plot where middle class well behaved white girl is whisked away makes for a good movie but paints a bad picture for how these situations actually happen.
It also makes them really hard to help as victims. Many of these victims have a hard time going to police due to former crimes themselves, don't trust the police, think they'll be laughed away, their captors had blackmail on them, etc.