A NIGHTCLUB hostess was gang raped by youths after she was abducted at knifepoint and knocked out with chloroform, the High Court heard yesterday. Tam Chun-ho, now 21, was the first youth to rape the woman after he won a ''cloth-scissor-stone'' game to determine who went first. He pleaded guilty to one count each of robbery and rape over the incident, which occurred 21/2 years ago in Tuen Mun. Deputy Judge Burrell adjourned sentencing to May 12 for a background report. Four other youths, aged 16 and 17, who also took part in the assault, have already been given prison terms ranging from four to 11 years. Prosecutor Philip Cantrill told the court that the 21-year-old woman was on her way home at about 1 am on October 1, 1991, when she was grabbed from behind by a man armed with a knife. She was taken to the intersection of Castle Peak Road and Tuen Mun Road, where the gang, including Tam, was waiting. The youths took $362 and her bank card before ordering her to walk to a construction site where she was knocked out with chloroform. After she collapsed, she was carried to a grassy area and one of the youths suggested they play the ''cloth-scissor-stone'' game so that the winner could abuse the unconscious woman first. Tam won the game and was the first to rape her. He was followed by other members of the gang. Some raped her while others indecently assaulted her. She came around in the middle of her ordeal, but feigned unconsciousness. Eventually the gang scattered in panic after hearing a police siren.