My first employer put profit sharing into an account managed by Fidelity. It was invested into a S&P 500 mutual fund. When I left them, I had forgotten about it. Fast forward, my current employer has their 401k account managed by Fidelity. At my first meeting to setup a 401k account, he asked for my SSN and DOB. That's when he discovered that old account. In almost 30 years, it had grown to $16,000. So it may pay to find out who administered your old 401k.