The first step to contact your old employer and ask to check their plan records to see if you participated in their 401(k) Plan. If it's not possible to get a hold of that employer, locate an old 401(k) statement to see if it contains contact information for the service provider that administered the plan. If none of those methods work, you can check The National Registry or the U.S. Department of Labor's Abandoned Plan Database to see if you have any account balances left unclaimed.