The incident happened around 10.39pm in Gill Lane, Longton.
Police say the 18-year-old youth was cycling along the road in the direction of Leyland when he was "involved in collision with an unknown vehicle which caused him to fall from his bike.
A spokesperson said the teenager was taken to Royal Preston Hospital with critical injuries which required surgery. He remains in hospital.
The other vehicle involved failed to stop at the scene and it is believed to have continued along the road towards Leyland.
Sgt Martin Wilcock of Lancashire Police’s Tac Ops Division, said: “Our thoughts are with the injured young man at this time.
“We are making a number of enquiries as part of our investigation into the collision, but we need to trace the driver of the other vehicle involved.
“If you were the driver I would urge you to search your conscience and do the right thing by coming forward so we can establish what happened.
“If you witnessed the collision or have any information at all that may help, please get in touch.”
Anyone with information should email [email protected] or call 101 quoting log number 1564 of 16th November.