A good starting point is to ask for the help of The Salvation Army
they will only take certain cases, however.
The Social Security
Administration will forward a letter for you under certain conditions.
Homeless-Missing
Persons Project
A good listing of services is available at Linkaway (I also
recommend their Homepage)
The Stalker's Home Page
You can pay for searches from Find a Friend, The National Association of
Investigatory Specialists, or Sherlock
Public Database searches from KnowX
Phonebooks
Nationwide Switchboard.com
More Phonebooks at 411.com
Also Phonebooks at 555-1212.com
Another Reverse
Phonebook
Lots of strange lookup info including whether a number is a cellphone
at Melissadata
Maps and Directions from Mapquest
More Maps, etc. from Yahoo
Missing
Persons Cyber Center A Bulletin Board of people who are searching