It's not going to be an easy task.
1. First of all, make sure you have the serial number or can otherwise positively identify the bike as yours.
2. Make sure you report the bike stolen to your local police, and again, if you have the serial number, this will allow entry into the national crime information database.
3. Post all the information about the stolen bike on social networking sites. Also tell your family members and friends as soon as possible.
4. Check your local Craigslist or other re-sell-it outlets.
5. Check local pawn shops. Here, most bikes are stolen by drug addicts and want to rapidly turn them over for cash.
6. Check local bike shops. Some buy used bikes.
If you ever find your bicycle on any site, inform the police instantly.