How do I find a 401k if the company in out of business?

This can be tough. There is no national clearing house that you can search for old 401(k)'s. If the company that sponsored the plan is poutr of business you need to find out who the administartor of the plan is, and contact them. This would be a bank, or an investment house, or maybe an insurance company. You should be receiving quarterly statements from them reporting your balance, so check your records at home and see if you can find an old statement. If not, then my suggestion is to contact your old boss or any old colleagues you may have kept in touch with and see if they know who the administrator is. If that doesn't help... another source is the National Registry of Unclaimed Retirement Benefits (NRURB). They are responsible with keeping over 50,000 individual retirement accounts for individuals who have forgotten 401(k), profit sharing and other company sponsored plan balances that have been abandoned. These assets are invested in the most conservative low yielding vehicles available, CD's and Money Market funds.
www.unclaimedretirementbenefits.com/doParticipantSearch.m
The final suggestion is go online and search for abandoned property in the state you lived in at the time. If you have not been receiving statements from the 401(k) plan administrator they may now consider you lost, and by law they would have turned your assets over to the state. Every state has a program to try to reunite people with their lost assets. Here is a free web site that lets you search your state's database of abandoned assets: Missing Money Free Search for Unclaimed Property - Officially endorsed By The States (http://www.missingmoney.com). It's a good idea to do a search on every state you ever lived in to see if there are abandoned assets in your name.