How do i find someone in specific because my friends dad left him before he was born and doesn't know his name or anything about him he wants to know if he can find him by using only the info he knows?

-Searching his last name on Facebook,
-Searching his last name in Google,
-Depends on the amount of info he knows....
-Ask mum maybe what his dads name was,
-If he doesn't know anything about him then why did you say "by using only the info he knows"?