The Ghetto Avenue Boys are a fictional boy band Randy Marsh joined in the 1980's. Randy told the whole story about his experience in the band to Stan in the Season Four episode, "Something You Can Do with Your Finger".
Randy's Boy Band
Randy started off by getting a gig when a record producer saw him performing in his high school's men's choir. He gives him a chance to join the band which he gladly accepts, leaving behind his final year of high school, his girlfriend, and his family to go record with four other guys he never met before. He was aware of how bad the songs were, but because of all the things he was granted with due to the public loving the songs, he stuck to it. Their big hit song was called "You Got It, Girl".
Speedy Spiral Downhill
When it felt it couldn't have gotten any better, their record studio had them replaced with the Avenue Ghetto Street Boys. All the riches he had soon went to rags as Randy had to move back to Colorado and face the mockeries of the townsfolk for being in a boy band.