Always easiest to just call the organization and ask. You should also check the National Registry of Unclaimed Retirement Benefits at www.unclaimedretirementbenefits.com. If it's been a long time, your prior employer make have moved your account here.
David, if you have an account somewhere you should be receiving statements that detail the contents of the account no less than annually. If you think you may have unclaimed funds somewhere, you can start here: www.unclaimed.org.
About how long does it take for an account to be move there?
This is a voluntary 3rd party account. Many employers keep terminated participants account, only some will transfer accounts to the Unclaimed Benefits program.