Well you have a year book right ?
You remember where they lived, so maybe you could walk directly to their home and politely introduce yourself to their family, and know if you could get their contact?
Just be like "I am a friend of your _____ from ____ and would like to know if you could give me their contact. Then if they say no, well here is my number, ( via card ) and if you could give tell them to get back to me it would be nice, thank you ( etc etc etc ).
Something like that.
You have to stop thinking about within facebook and bs like that. Maybe they had an Myspace, or maybe they even used their old phone number. Not everybody is best at communicating via electronics.
In fact a lot of people are disturbed by Messaging ( electronics ) and does not see those people as nothing but robots, or not real people. So contacting them via online might not actually be helpful to your advantage.
You have to talk with them on the phone, or literally face to face.
Like a job interview. Some people might turn away from you once they realize your not a "money person" or even might freak.
Another issue is
You have people who might be of X-Religion/Race/Culture and they have become alienated or brainwashed over time. They opt to make a choice that everyone is stupid, or they themselves is stupid, and have low self-a-steem to the point of just accepting one of those the norm or living a type of sheltered life.
So chances are they still go to the same events but now blend in with the normies because they have given up on associating people outside" their means of survival".
Like you have men married to women who are haters of men but are with them due to financial, cultural, or racial concerns. You have women married to men who have been outcasted, or they themselves are openly racist, or even controlling or have power over them. You have people who have shut themselves from the world for X reason and only associates they had was their co-workers or class-mates. Slaves since the day they came out of the womb.
Personally I make friends via my work, and area of studies. Beyond that it is impossible without money or looking like a value myself. Reaching out to many people from my college years have been backfiring because all of the pro-accept everything kinda fails and they fall back into being humans who are needy.