I spent 30 years in the military the first thing I would do would be to make contact with the military service he is in if you know. The military normally takes a dim view of its members when they bring discredit on the service by not taking care of their financial obligations.
If you are starting a legal action in court, the law may require you to file an affidavit stating the military status of the parties in your case. To find out if someone is in the U.S. military on active duty, contact the following agency:
Defense Manpower Data Center Attn: Military Verification 1600 Wilson Blvd., Suite 400 Arlington, VA 22209-2593 Tel: (703)696-6762 or -5790 Fax: (703)696-4156