Officials released a picture of a white Ford F-150 and said they wanted to talk to the driver, but stopped short of calling the person a suspect.
The vehicle was spotted around the time the fire broke out in an Orange County canyon, according to county fire Chief Chip Prather.
Authorities began looking for the truck, believed to have been made between 1998 and 2004, based on information received from a tip line. Additional details were not released.
The fire has burned 27,600 acres and destroyed 14 homes in the foothills east of Irvine.
Authorities believe the blaze was deliberately set because they found two ignition points within a short distance - a common sign of arson.
About 55 agents from the Bureau of Alcohol, Tobacco and Firearms, as well as the FBI, have joined the investigation. Officials have received some 700 tips and offered at least $250,000 in rewards in the case.
At least five people have been arrested and booked for investigation of arson since wildfires broke out across Southern California this week, though none has been linked to any of the major blazes.
In one case, a man suspected of starting a fire on a San Fernando Valley hillside pleaded not guilty Friday to one count of arson.
Catalino Pineda, a Guatemala native, was being held on $75,000 bail and scheduled to return to court Nov. 7.
Police said witnesses saw Pineda, 41, start a fire Wednesday in the West Hills area of Los Angeles and then walk away. Witnesses contacted authorities and followed him to a nearby restaurant where police arrested him.
Pineda is currently on probation for making excessive false emergency reports to law enforcement, police said.
If convicted of the arson count, he faces up to six years in prison.