Sign up for social networking websites such as Myspace or Facebook.
Try to enter an old college email address for the friend (if you still have it) in the social service's friend finder. She might have signed up using the inactive email address, so you might be able to locate her this way.
Type the friend's first and last name into the search engine of the social site. Do not limit your search by entering in a location or any other specifics, as these might have changed since you last saw him. Search through the results (and the photos of the results) until you find your friend's profile.
Hire a private detective if your friend does not have a profile online. A detective will be able to search through public records to track down your friend, sometimes in just a matter of days.