No one is supposed to post info on living people here.
And without more info: like where you are from, what circumstances separated you, and if he is supposed to be alive and when/where last you saw him, we couldn't help.
Try searching for his name, try checking people.yahoo.com, whitepages.com & zabasearch. If you are young, try your paternal grandparents if you know them. If you are in the US you can try writing a letter for the SS Administration to send on to him - they do this in case of emergencies and will read the letter. If your parents were married and are no longer then you should have a last known address, and potential names of his friends there, that you can ask if they have heard from him.