If you think that you are owed unpaid back wages held by the US Department of Labor Wage and Hour Division there is a site where you can search. From the site:
The Wage and Hour Division (WHD) enforces some of our nation's most comprehensive labor laws. When we find violations, we often recover unpaid wages on behalf of employees. The agency makes every effort to locate and notify all employees due back wages. If we cannot find an employee, we hold their back wages for three years while we continue our efforts to locate them. After three years, if we remain unable to find the person, we are required to send the money to the U.S. Treasury.