The Ventura County Fire Department says the vehicle went over the side of a road on Saturday in the area of Deer Creek Road and Pacific Coast Highway.
One occupant was able to get out of the vehicle and left the scene in another vehicle, without calling 911, VCFD says.
But on Monday that person returned to the scene and reported two missing people who were in the car at the time.
Shortly after a search team was dispatched, they were able to determine one of the missing occupants was safe at home.
A search continues for the other missing person.
It was not immediately clear why the driver failed to report the incident or the missing persons immediately after the crash.
Authorities were using a helicopter, drones, K-9 teams and search-and-rescue crews to search for the missing individual at night.