In fact sometimes people (like Class Reunion Organizers) have to try and figure out how to find a couple of hundred of people 5, 10 or 20 years after graduation---Throw in a few name changes, and the task can seem daunting.
Fortunately, many schools keep alumni databases that are searchable by fellow alumni and there are several public record data-bases that make it easy---I encourage you to find all possible online sources to find these old friends---Check out sites like facebook, myspace, and classmates.com And check out the other tips you'll find on this website