There is no centralized system that tracks pension and 401(K) plan information.
According to Ellen Bruce, associate director of the Gerontology Institute at the University of Boston, the value of lost pensions runs "over $10B easily"
There are many reasons why so many are lost: increased mobility, non-portability, frequent corporate mergers and sloppy record keeping.
The June AARP Bulletin notes that Bruce and a colleague advocate creating a centralized registry to track pension information in the Spring issue of The John Marshall Law Review which has not yet posted online.
You know you should keep track of your past employers as well as your current ones. But that can be hard if you don't know if or when mergers have occurred or who is responsible for pensions.
If you think you have lost a pension to which you are entitled: