Tips to aid your search:
If you know where someone works or has worked it's possible that you might find their names listed on a company or organisation's website or you could could try to send a request for information to that site.
For example, I was able to contact a cousin of mine in the United States by searching through staff listings on school websites in the area where I knew she worked!
Surprisingly, this is not the first site to try and help people find their missing others!
I have found several which you could try, many are American and some charge for their services but only you can decide if your search is worth the investment!
If the person you're searching for has contributed to discussion within an Internet newsgroup then you may be able to find their email address by using this newsgroup search facility:-
Sites offering links and tips to aid your search:-
Lookup United Kingdom – Genealogy, adoptee and birth parent search, lost friends and family.
Gone Missing UK a website to help locate missing persons everywhere, specialising in the Yorkshire area of England, UK.
Joan Allan's Search Site
A comprehensive site offering lots of useful information and links to other agencies and its own "Search and Advice services" which may incur charges.
Friends Reunited A UK site specialising in reuniting old school and college friends.
Find lost friends classmates and other missing persons
Some American commercial sites:-
Find People Fast-Search Locate Missing Family
Some sites offer directory and listing services such as email addresses and phone numbers. You may be lucky to find someone by checking these out.
Phone Numbers & Addresses
Four11 Directory Services
If you are unfortunate to have lost contact with someone through war or a political situation, then you may want to contact the following organisations:-
The American Red Cross
They have an on-going project to help find victims of the holocaust and second world war.