You need to file a motion for enforcement in the court that issued the child support order (unless certain things have changed). You need to draft it, file it, serve him with it, and have a hearing. You'll also need a statement from the AG showing he's delinquent.
I'd strongly recommend consulting a local attorney as the pleadings are tough in this one.
While I agree with Mark Cohan that hiring a private attorney to assist is the best approach, a less expensive recommendation is to consult with your local office of the state Attorney General's office. They are in the business of enforcing child support awards. The good news: they are practically free; the bad news: they have lots of cases, so you'll probably get quicker service from a private attorney.