Kidnapper's car found on Sydney fringe The car used in the knifepoint abduction of a baby boy from a Sydney home has been found abandoned southwest of the city. Police say a man, 24, armed with a knife forced his way into the house on Kenthurst Place at Chester Hill about 8.30pm on Thursday. The man grabbed a 16-year-old and his eight-month-old son and put them in the back of his black Toyota Camry. The man stopped the car on the Hume Highway at Douglas Park about 10pm and assaulted the girl. He drove off with the baby still in the car. A police spokeswoman told AAP the man's car was found about 6.50am on Avon Dam Road at Bargo. She says no one was found in or near the vehicle. A search is "now underway for the 24-year-old man and his infant son," the spokeswoman said. The kidnapper is described as being Caucasian, about 165-175cm tall, with brown hair and wearing a blue jumper and green track pants. Police are concerned about the boy's welfare and are seeking urgent assistance from the public to locate him.