The incident unfolded at about 10 p.m. as the victim was sitting in the car, a Honda Civic, with three other people in a drug store parking lot near 15th Avenue SW and SW Roxbury Street.
There was some kind of verbal altercation between the people in the car and a group of pedestrians in the parking lot. As the car was driving away, one person in the group of pedestrians pulled out a gun and opened fire at the rear of the car, said Cindi West of the King County Sheriff's Office.
One bullet penetrated the right rear taillight, striking the teen in the back. None of the others in the car was hit, said a King County sheriff's sergeant at the scene.
The shooter and other pedestrians fled the scene on foot.
Friends took the victim to a fire station, and he was rushed to Harborview Medical Center in Seattle, where he died.
Police responded and searched the area. They found three shell casings near the intersection of 15th Avenue SW and SW Roxbury Street.
King County sheriff's deputies are looking for the shooter. A description was not immediately available.