The shooting happened about 9:30 p.m. Tuesday at Gardendale Street and Dakota Avenue, just off Garfield Avenue.
Los Angeles County Sheriff's homicide investigators said the teen, identified as Roxy Borboa Galindo, was in a car with four males when someone fired a handgun at the car. The bullet went through the back window and hit the teen in the head.
The driver tried to find the nearest hospital but eventually stopped near Magnolia and Alpine avenues in Lynwood to call deputies for help. The victim was rushed by paramedics to St. Francis Medical Center, where she died shortly before 3:30 a.m. Wednesday.
The male driver and a male passenger in the vehicle were not injured.
Investigators were searching for a suspect. The motive and circumstances surrounding the shooting remain unclear. It's unknown whether the car was targeted or if it was involved in a random shooting. Investigators said Galindo had no known gang ties.
Citing South Gate police, sheriff's LT. Mike Rossen said there was new graffiti near where the shooting took place, and that is being looked into as a possible motive for the shooting.
Galindo attended Bell High School. Her friends at the school were grieving her death. They said they learned of her death through Facebook and other friends.
"She was amazing. She was the sweetest person you'd know," said Natalie Sanchez, a childhood friend of Galindo. "I broke down. I didn't want to come to school because it's nerve-racking. She's gone. I can't imagine her being gone, of all people."
Detectives said a late 1990s, dark-colored SUV similar to a Chevrolet Blazer or Ford Explorer may have been involved in the shooting. They said they hope surveillance cameras from a paper company in the area may give them more clues and help them find the gunman.
Anyone with information regarding this crime is urged to contact the Los Angeles County Sheriff's Department's Homicide Bureau at (323) 890-5500.
Correction: It was earlier reported that the victim was 19 years old. Authorities say she is 16.