General synonyms:
* Smuggler
* Moonshiner (specifically for alcohol)
* Trafficker
* Counterfeiter
* Black marketeer
* Runner
* Dealer
* Peddler
More informal synonyms:
* Hoodlum
* Racket
* Souse (for alcohol)
* Rumrunner
The best synonym to use will depend on the specific context of the situation and the type of illegal activity being discussed.