Find my401k pension

It is in and with the investment company you placed it in. It is in the company that would send you at least a annual report every year and most likely a quarterly report each year.

If you don't remember you contact the HR department where you worked and ask them who was the admin of the program.

Also the company is required to report any retirement benefits you have with any company. So when you file for social Security they will inform you about any 401K accounts you have.