If your case is a civil collection / small claim that has gone to judgment there is something called a Capias, which is a civil arrest warrant. Most of the time a Sheriff or Constable will just call you and tell you to be in Court at a certain date and time, but there are occassions where a sheriff or constable has been authorized to physically bring a person into Court..what you might characterize as an arrest. Generally a capias is only issued when there have been no to very little payments and at least one missed Court hearings.
Depending on whether you can prove the harassment and that he called your employer, you might have a case under the Massachusetts Fair Debt Collection Practices Act. Unlike the federal law, the Massachusetts law applies to the original creditor, too. His actions might also be "unfair and deceptive" within the meaning of Chapter 93A of the Massachusetts laws. The fastest way to stop the harassment probably is to hire a lawyer. Once the lawyer tells the creditor that the lawyer has been hired, the law requires the creditor to stop contacting you. Some creditors don't obey the law (obviously), but an aggressive lawyer should be able to stop it pretty quickly. Unfortunately you would have to pay a retainer, and it sounds like you might not be able to do so. If that is the case, you might want to contact the Volunteer Lawyers Project in Boston for help, which is free. Good luck!
A creditor cannot threaten you with arrest or inform others of your debt. You will not be arrested unless you fail to show up to court or refuse to pay when you clearly have the money to do so.