Anita, if you have funds in a 401(k), and the company closes, it is still your money, But you need to find it.
Every plan has a plan administrator, that, as the name implies, administers the plan. If a plan is terminated, the undistributed assets go to a Qualified Termination Administrator, or QTA.
The Employee Benefits Security Administration, or EBSA, is run by the Department of Labor. EBSA keeps track of who the QTA would be.
Just go to http://askebsa.dol.gov/AbandonedPlanSearch/ and find your plan.
If you had a pension under the same circumstances, you would go th the Pension Benefit Guaranty Corp website at http://pbgc.gov/.
I would also check on you states website for unclaimed money. In Florida, it is https://www.fltreasurehunt.org/