Zdeno Mirga, 18, was convicted of eight counts of rape by a jury at the Old Bailey yesterday.
Two boys, who cannot be named for legal reasons, were also convicted of various counts of rape and sexual assault.
A 13-year-old victim described during the trial how she was forced to have sex with a number of different men.
Prosecutor Angela Rafferty said,"He (Mirga) encouraged her, often very forcefully indeed. He did this using the power he had over her at the time, or threatened her and sometimes he used violence against her."
A jury is considering the remaining charge against Zdeno Mirga of inciting a child to engage in prostitution as well as charges against Hassan Abdulla, 33, and another boy.
Judge John Bevan gave a majority instruction to the jury.