And yes, it is a pay as you go program, not an investment program..
"The current Social Security program is a defined benefit social insurance program. A worker and eligible dependents receive monthly benefits based on a formula that takes into account the worker's earnings history. Financing of the program is pay-as-you-go. The payroll contributions of workers each month help provide these benefits to eligible retirees, disabled workers, and survivors in the same month. "
https://www.ssa.gov/oact/solvency/provisions/individualaccts.html