The leader of a gang-run prostitution ring that recruited girls as young as 15 years old in Riverside and surrounding cities is facing 30 years in prison after admitting he was guilty of sex trafficking and other charges.   Paul Edward Bell, 29, of Lynwood was the eighth and final defendant to plead guilty or be convicted in connection with the sex-for-money operation busted by local, state and federal law enforcement officials in July 2012.