A 2009 grey Acura TSX was westbound on Highland Boulevard in Cypress Hills when it collided with the moped just before 10 p.m. Monday.
When police arrived, they found two people from the motorcycle injured.
An unidentified man was ejected and suffered severe head trauma, and a 17-year-old was stabbed multiple times.
Both were taken to Brookdale University Hospital in critical condition.
The driver of the Acura with Pennsylvania license plates fled the scene and is being sought for questioning.
Detectives are looking into the stabbing as the possible result of the crash.
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