Prostitution is legal and regulated in Singapore, where Geylang is. It is illegal for an employer to hold a passport. It is a dangerous area, I know a similar case where a lawyer from HK paid Pounds Sterling 10,000 to free a girl, both of them were then murdered. Go to a lawyer, preferably a woman, they are stronger than men (I am a male lawyer!) and get her advice. If the girl owes money legally, then under the contract she may have to pay the money. BUT she should get her passport back regardless. Your lawyer will say if the Police should or should not be involved as a matter of common sense. Police are not immune from corruption in any country. If you are not a Singapore National, your Embassy might help. Finally ( do not get mad at me, this is good advice) make certain the girl is not trying to rip you off. OK? Good luck, your motives are fine but do be careful.
The search for people who can answer your question continues for as long as needed - until you find the answer you were looking for.
When an answer is posted by someone who was invited (byYedda or by yourself) to answer your question, their answer is marked with a yellow "invited by Yedda".
To be invited to answer other people's questions in your areas of knowledge and interest, be sure to list your favorite topics:
» My Settings My Topics.
Of course, the more helpful your answers are, the more likely you are to be invited to future questions...