If you're trying to find someone on the Internet, there are several
Gopher and Telnet sites that collect the email addresses and names of
users on the Internet.
This will enable you to use a command-line to search for a variety of
information. You can enter commands like "query clark" to look
for someone with that last name. This interface is not for the faint
of heart, though.
If you haven't found the person you are looking for, you might want to
also check here. From Yale University, this is a listing of other white pages
services.