There are quite a few additional tips that I can give you to teach you how to find family, friends, classmates, old-colleagues and ex-military friends online. The first thing you should do is be sure to have as much information about the person before you start the search---Things like First Name, Last Name, Aliases, Maiden Name, Middle Name, names of family members and children and (ex) spouses.
It may also be helpful to know what schools the person has attended (the person in charge of the high school reunions is frequently easy to find and may have the address or phone number that you are looking for).
Start with whitepages.com or yahoo people search -- These options work best if the people haven't moved in some time and actually have a listed residence with their local phone company. You may also be able to do a reverse-phone number search by googling their telephone number and seeing what google delivers.
Check Social Networking Sites---If the person has an uncommon name, you may be able to find them on facebook.com or myspace. If you know what company they worked for, you'll be able to conduct a search on linkedin.com to try and find the person's current where-abouts.
Check other sites---Some sites that may be useful to you include zabasearch.com and zoominfo.
Reach out to old neighbors and friends--If online services don't solve your problem, you can try and find other old friends, neighbors, or coworkers of the person and ask them for help---It's like 6 degrees of separation---your chances of finding a person increases if other people know that you're looking for somebody.
