The SS "lock box" is empty, nothing but IOUs. In order to pay back those IOUs and cut checks currently going out, the SS tax that everyone working pays is supposed to cover this, supposed too anyway. The problem is that it doesn't and it won't going forward.
People who say they've paid in for X number of years and want their money back need to talk to their representatives, because their money is gone. There is no fund full of the 2.5 Trillion or so for SS, the money has been spent. If not enough people are working and paying SS taxes, the people currently getting SS checks will not be fully covered, and the general fund and income taxes pick up the difference.