Fontana police were searching for 19-year-old Daniel Gamboa, 18-year-old Kasey Vance and 17-year-old Samantha Ornelas, who were reported missing by their families.
Officials said the teens told family members on Saturday they were going to the Angeles National Forest, possibly near Mount Wilson.
The Los Angeles County Fire Department said while searching for the teenagers, a helicopter with the Los Angeles County Sheriff's Department spotted a truck that appeared to have crashed over the side of Angeles Crest Highway at mile marker 40, approximately two miles from Mount Wilson Road.
According to fire officials, three people were pronounced dead at the scene.
Video from near the scene of the crash showed family members of the missing teenagers on their knees praying and crying in agony.
Authorities said some of the victims were ejected during the crash.
The three teens were believed to be in Gamboa's white 2008 Toyota Tundra pickup truck. The vehicle that crashed over the cliff appeared to be a white truck, according to video captured at the scene from AIR7 HD.
Gamboa's tailgate also featured a distinct logo, according to Fontana police. A tailgate appearing to have that same logo was spotted at the scene of the crash.
When emergency crews first responded to the scene, they were only able to confirm two people were dead. A third person was later confirmed dead at about 6:30 p.m.
Family members of the missing teenagers said they were still awaiting for the bodies found at the scene to be positively identified.