Unfortunately, NH is one of those states that do not license contractors at a state level. You can file a complaint with the NH Consumer Protection Bureau for all the good that will do you.
https://www.doj.nh.gov/consumer/complaints/index.htm
Also check with your city or county to see if a local license is required and whether he has one.
You can sue him but, even if you win, collecting from scammers is often problematic.
But, bottom line, I think you may be kissing your money goodbye.
Life lesson from the school of hard knocks: Never give any contractor or workman any money up front. Always pay on completion, even you you have to buy the materials yourself.