The three-car crash occurred near Crenshaw Boulevard around 4:02 a.m.
Authorities traveling westbound on the 105 Freeway found an overturned pickup truck and an overturned Range Rover.
A girl who was ejected from the pickup truck was found trapped underneath.
Responding officers and Good Samaritans rushed to the scene and helped push the pickup truck off the girl, who at one point was laying face down and unresponsive.
Authorities said the juvenile suffered lacerations to her face and head. She and three other occupants of the pickup truck were transported to local hospitals. Their conditions remain unknown.
None of the occupants in the Range Rover were injured.
No description of the hit-and-run motorist was released.
The investigation is ongoing. Anyone with information regarding the hit-and-run driver was urged to contact the CHP at (310) 642-3939.
CNS contributed to this report.