I have a lot of experience dealing with Identiy Theft. Since 2003.
1)Forget about catching the criminal. I had the guys address (he took out a mortgage loan) and the cops wouldn't do anything about it. I was tempted to drive the 2000 miles to his house and punch him in the face. He apparently moves from state to state a lot though.
-I'm even able to track his location based on unpaid taxes from mulitple jobs. Pretty easy to tell he's a migrant worker.
2)When dealing with the IRS you will eventually get assigned an identity theft agent. It could take years for you to get one. They require multiple instances of identity theft before they take you seriously. (ie had unpaid taxes filed on mulitple years). Even then you will have to dispute your tax filings every single year. Make sure you don't get a refund. It's usually October before the IRS (from mulitple departments) is satisfied.
3)The IRS will assign you a pin. You will need to use the pin, along with your social security number.
4)Getting a new social security number is pointless. It does nothing. Both numbers, by law, will be valid until you die if you get a second one. The IRS can't lock your number, but they can put a warning on it.
5)Lock your credit. Call all 3 companies. This puts a hold on all credit applications to contact you for confirmation. Start disputing all charges. This also could take years. Credit rating hit 0. That's right. Zero. Didn't know it could be that low. Took 7 yrs to get back to normal.
-If you get frustrated, use an identity theft service. You pay money for a company to moniter your information for you. They will check your credit every 4 months. You can do it for free yourself though.
6)Hope it's not an "undocumented worker" that is using your ID to stay in the country. If it is, this will be something you will have to deal with for the rest of his stay in the country. Thanks Obama for not deporting these "harmless" people!
7)Making it easier: Accept your new reality. There are now two of you. Like dealing with a chronic injury this will be the pain in your ass for the rest of your life. Take a zen attitude. Voting Republican might help too.
If this is a one time thing, count yourself lucky.