It happened at 10:50 p.m. Monday on Chester Pike at Sellers Avenue in Ridley Park.
Police say 18-year-old Christopher Brooks of Crum Creek Drive in Woodlyn was either riding his bicycle or walking it across an intersection when he was struck by a gray or silver pickup truck.
Brooks was not wearing a helmet and suffered head injuries and a broken leg.
Medics rushed him Crozer Chester Medical Center in critical condition.
Police are now looking for the striking vehicle, possibly a Ford F-150 pickup truck.
Surveillance video from a home security system released by police early Tuesday morning shows the truck's headlights driving past the camera moments before the accident.
Investigators say the truck did sustain front-end damage in the collision. They are working to get more identifying information from a piece of the vehicle's bug deflector that was left at the scene.
They are also checking surveillance video from nearby Taylor Hospital for more clues.
Anyone with information about the accident or the motorist is asked to call Ridley Park Police at (610) 362-7401.