The crash also killed Walker's friend and financial adviser Roger Rodas, according to Walker's publicist, Ame Van Iden. She said Walker was a passenger in the car when the two drove away in a 2005 red Porsche Carrera GT from a fundraiser in the community of Valencia, about 30 miles northwest of downtown Los Angeles.
Sheriff's deputies found the car engulfed in flames when they arrived at the site of the crash, near the fundraiser at Rodas' sport car dealership. Officials have not identified either person found in the car.
On Sunday, fans of Walker, 40, gathered to leave flowers, candles and memorabilia from the action movies.
Walker is "gone but he'll never be forgotten because there are so many people that look up to him," Joel Perez, 23, told the Los Angeles Times at the memorial.
Sheriff's deputy Peter Gomez said investigators are working to determine how fast the car was traveling and what caused it to go out of control, including whether the driver was distracted or something in the road prompted him to swerve.
After the Porsche crashed into a light pole and tree, it burst into flames. The downed light pole had a speed limit sign of 45 mph.
Walker rode the "Fast & Furious" franchise to fame, starring in all but one of the six action blockbusters, beginning with the first film in 2001. He had been on break from shooting the seventh installment; production began in September and while much of the film has been shot, it's incomplete.
Universal Pictures has not said what it plans to do with "Fast & Furious 7," which currently is slated for release in July.
Walker and Rodas had attended a fundraiser benefiting victims of the recent typhoon in the Philippines. The event was held by Walker's Reach Out Worldwide, a charity he founded in 2010 to aid victims of natural disasters.
The fundraiser and toy drive took place at Rodas' custom car shop, Always Evolving. Attendees rushed to the nearby crash to try to put out the flames with fire extinguishers.
Bill Townsend, who attended the event, told AP Radio that Walker appeared very happy at the fundraiser.
"He was smiling at everybody, just tickled that all these people came out to support this charity," Townsend said. "He was doing what he loved. He was surrounded by friends, surrounded by cars."
Walker left behind two completed films. He stars in the upcoming Hurricane Katrina drama "Hours," which Lionsgate's Pantelion Films is to release Dec. 13. He also stars in "Brick Mansions," a remake of the French action film "District B13" that Relativity plans to release next year.
His "Fast & Furious" co-stars reacted in shock the actor's death. Vin Diesel posted a photograph of him and Walker arm-in-arm on Instagram with the message: "I am absolutely speechless." Lucadris said on Twitter: "Wherever you blessed your presence you always left a mark, we were like brothers."
Walker is survived by his 15-year-old daughter.