Wow. So presumably employee and employer contributions were directed to an investment advisor and now the funds cannot be accounted for? That's not good. The money went SOMEWHERE.
I suggest you contact the federal Department of Labor (who have jurisdiction over employer-sponsored retirement plans) and see if they can help you. 202-693-4650.
Are you sure you never received any distribution for which you were eligible after you left that employer? I have had long-gone employees contact me insisting they never received funds from the 401(k) after they left when, in fact, we could produce a copy of the check that was mailed to them years before.
A person, who is nice to you, but rude to a waiter, is not a nice person. (This is very important. Pay attention. It never fails.)