Throughout the series, it was never mentioned what happened to Sonny's father or where he is.
(Sonny runs into Chad)
Chad: Hey Sonny! What are you uh... what are you doing here?
Sonny: Um, I kind of work here. What are you doing on the "So Random" stage?
Chad: Oh, I think I left my glasses here.
Sonny: You don't wear glasses.
Chad: Sunglasses. That I wore to the beach when we were dating.
Sonny: Yeah well, maybe um, maybe you should try the beach!
Chad: Hey um, but you know the thing is I just really miss those glasses, you know?
Sonny: Well um, maybe if you had let those sunglasses have their moment in the sun, they wouldn't have broken up with you!