Legal Question in Criminal Law in Massachusetts

Re: theft

You could call the society for prevention of cruelty to animals. Or call your local legislator, the office of the district attorney, or even the police chief, or the town administrator.

Re: theft

Under the law, pets are treated as personal property (much like, say, your bicycle would be treated). If you have evidence to prove the dog is yours, I think you should sue in small claims court. The process is relatively easy, and you probably won't need a lawyer. I suggest you contact the small claims court in your jurisdiction and ask about how to file a case.