Unless you took the money out, it should be, and it should be sending you at least a annual notice.

You contact the plan administrator for your 401K

It's possible that if you left the job where you had the 401(k) account and your balance was below a certain amount (typically $5K), the plan administrator would have automatically distributed the funds to you. But then you should have received a distribution check, and a 1099-R form to file with your tax return. If you're sure this did not happen, then the account should still be open. Like Fr_Chuck suggested - contact the plan administrator. You should be able to find contact information printed on any of your old account statements.