Keep in mind he did say he was searching for the former students of a class and its 5oth class reunion
If we're talking high school reunion then we're talking about persons in excess of 66 years old. Worse... if we're talking about a college reunion then add at least 4 more years to the formula.
I'm not sure if Facebook would be the most appropriate place to look.
The networking via former friends and family would be the only viable method of contacting those difficult to find. And sadly enough, one could also cross some names off my researching the obits of one's local newspaper.