Since 401(k)s could have been managed by either a trust company, a bank, or even by your own employer, it could be impossible to locate the plan you participated in, especially if it was managed by your company itself.
As LEV noted, each plan is required to file Form 5500 with the IRS, but if you don't know the name of the plan, it will be impossible to find it,
The government does not keep or track private retirement accounts; that is your responsibility as the privacy freaks have made sure that the government stays out of that business as much as possible.
If your funds were rolled over to an IRA, then each year you have an IRA, the trustee is supposed to report the year-end balance to the IRS on Form 5498. You might check with the IRS(NNN) NNN-NNNNand see if someone has been sending this form to the IRS each year. You might not have received a copy because the trustee has an incorrect address, but at the IRS, these are kept by your SSN. So call them and see if there are any unknown Forms 5498 in your account.
Generally, if your company managed the 401(k), they likely transferred any balances to a private company before they closed.
Your last statements from this account should give you some clue as to where to start looking.