Billy Circlovich only appears with a voice in one episode, "The Tooth Fairy Tats 2000". He isn't seen at South Park elementary school so he is most likely attending another school. He looks around 8-9 years of age and is seen again for the second and last time in the episode "The Wacky Molestation Adventure", where he is seen in the background along with other children waiting for his parents.
He appears very sickly, with bags under his eyes and sunken in cheeks. He has brown hair. He wears a green shirt and blue jeans.