Hire a lawyer to send a cease and desist letter. You can't issue a subpoena unless a case is pending.
I am a former federal and State prosecutor and have been doing criminal defense work for over 16 years. I was named to the Super Lawyers list as one of the top attorneys in New York for 2012 and 2013. No more than 5 percent of the lawyers in the state are selected by Super Lawyers. Martindale-Hubbell has given me its highest rating - AV Preeminent - in the areas of Criminal Law, Personal Injury, and Litigation. According to Martindale-Hubbell”AV Preeminent is a significant rating accomplishment - a testament to the fact that a lawyer's peers rank him or her at the highest level of professional excellence." Fewer than 8% of attorneys achieve an AV Preeminent rating. I also have the highest ranking – “superb” – on Avvo. The above answer, and any follow up comments or emails is for informational purposes only and not meant as legal advice.
Hire a lawyer - or maybe contact the police - although I don't know how much they could or would do.
Best of luck.
Joseph L. Ciaccio is a New York attorney with the Law Offices of Joseph M. Lichtenstein, P.C. (medicalattorneyny.com). The answers posted herein are not legal advice and do not create an attorney-client relationship.