You should be contacting law enforcement immediately with any and all information you have.
This answer is only for informational purposes and is not meant as legal advice.
If you have reason to believe a person is being held against their will, I would also recommend you contacting the authorities. If you want to hire someone to help locate the individual, yiu can look for a private investigator that specializes in that sort of thing.
I am a former Brooklyn Criminal Court Deputy Bureau Chief with over 17 years experience specializing in handling criminal cases. All answers are for information purposes only. Answering this question or any future questions does not form any attorney-client relationship. Be mindful, that answers are limited by the limited facts presented by the questioner and are not meant to take the place of competent legal advice by an attorney fully informed of all the facts surrounding your case. Also, be aware that nothing posted in a public forum such as this can be deemed confidential or privileged communication.