A faceboo is someone you have an online relationship with. You'll probably never meet your faceboo in person, especially if he or she lives in another state or even another country, but you still flirt on various social media.
So when you gonna hook up with that girl you keep chattin with?
Chill, son - she just my faceboo.
Yo, you know those friends on Facebook, friends of friends, people you don't know, but they always be likin yo posts, sending Happy Birthday or commenting on yo club pics? They yo faceboos. You have ya bros, ya hos, ya boos, ya cuz and ya faceboos.