Ricardo Ramirez Jr., from the Bay Area, was fatally shot on July 13 at around 10:30 p.m. by a vice sergeant.
His family said he had just graduated high school and was in Los Angeles vacationing with friends.
On Wednesday, his family and friends gathered in front of LAPD headquarters in downtown L.A. to demand justice.
"The best brother, so young," said Larissa Ramirez about her younger brother. "He was so kind. So funny."
The family's attorney says Ramirez was riding in a silver Cadillac with three other men near the Figueroa Corridor when they noticed a dark unmarked vehicle with tinted windows following them.
After stopping, Ramirez and another passenger got out of the car with their palms raised to ask why they were being followed, that's when Ramirez was shot in the chest.
"This shot came from within the car, through glass - meaning that Ricky didn't even have an opportunity to see someone in the car pointing a gun at him, much less somebody he would identify as a police officer," said Christopher Dolan, founder and chief legal counsel of the Dolan Law Firm, which is representing the family.
An LAPD press release says vice officers in plain clothes were conducting prostitution enforcement nearby. They say no firearms or other weapons were found during the investigation.
Ricky's family say they are filing a lawsuit against the city, the department and the officer involved in the shooting.
"I just buried my son a day ago. That was the hardest thing a mother could ever do," said Renee Villalobos, Ramirez's mother. "And to know that he died for no reason, it makes no sense. It is not fair."
"When it comes to real life, you never expect to receive a phone call and receiving this news," said his father, Ricardo Ramirez Sr. "Like my wife said, he was just 18 years old. His journey was just beginning and that was taken away from us."
The LAPD says officers from the Force Investigation Division and representatives from the California Department of Justice are looking into this incident.