It happened just before 11.30pm when a Yamaha motorcycle came off the road between Otley and Bramhope and collided with a dry stone wall.
Also in news: Robbers left man with fractured jaw after brutal Leeds street attackPolice said the motorbike had been travelling towards Leeds on the A660 Leeds Road at the time.
The 19-year-old rider suffered serious injuries and was taken to Leeds General Infirmary for treatment.
A spokesman said Eastern Area Roads Policing Unit officers now want to speak to anyone who witnessed the incident
"The rider had been travelling with two other bikes when the incident occurred," he said.
Also in news: Three men released after Morley stabbing remain 'under investigation'Anyone who saw the incident or the manner in which the motorbike was being ridden just prior to the collision is asked to contact the Eastern Area Roads Policing Unit on 101, referencing police log 2197 of June 4.