The incident occurred just north of Tuxford Street around 4:20 a.m.
Police say Blake Cook, 18, of Saugus was a passenger in a Honda Accord that collided with a tractor-trailer.
When another car slammed into the tractor-trailer, Cook got out of the Honda and attempted to run across the traffic lanes to the side of the freeway. That's when he was hit by a big rig that immediately left the scene.
Cook was pronounced dead at the scene. He was a resident of the Saugus neighborhood in Santa Clarita and a Valencia High School senior.
The driver of the Honda Cook was riding in, identified as 20-year-old Eddie Camargo of Saugus, was arrested on suspicion of driving under the influence of drugs.
Shedding tears and leaning on each other for support, dozens of teenagers gathered in Cook's honor in Saugus Saturday night.
Cook's friend, Kaley Frias, was shocked to hear of his death.
"Can't even express how much that kid would do anything for anybody, like, he just always had so much positivity about him," said Frias.
"He was just like a happy kid, he always looked at the bright side of everything," said Cook's friend, Shaun Pierce. "He was always there for me whenever I needed him."
Cook's friends urged the driver of the big rig that left the scene to turn himself in.
"He was just trying to get out of a car crash, he's just trying to get to safety, and they killed him, and just kept going like it was nothing," said Pierce. "They should have a guilty conscience."
Anyone with information on the incident was urged to contact CHP.