Try using a search engine like google, yahoo, or others to find your old friend. If you know the city, that may help.
Social networking sites including myspace.com; facebook.com; and yearbook.com will also provide opportunities to find old schoolmates. Photos and other information are generally also available.
Sites including classmates.com or reunion.com can help locate friends by your high school. If your school mates are registered users, you can send an email directly to them.
Check with your high school guidance or alumni office. They may have a networking service to connect old friends. Also, if there is a reunion committee, they may also have contact information.
There are also the old-fashioned ways to find friends you've haven't seen since your teens, too. One is the good old white pages. If you insist on being tech savvy, try using whitepages.com or whowhere.com and plug in your friend’s first and last name. It may be just that easy. Why not keep in as simple as can be? Why not call that old high school phone number. His or her parents may still live there. They would of course of the friend's contact info.