(CNN) The boy who made headlines when he was photographed hugging an officer during a 2014 protest against police brutality is missing after his family's SUV plunged 100 feet off a coastal highway in California, officials said Wednesday.

The bodies of Jennifer and Sarah Hart, of Washington, and three of their six children, were found Monday in and around the vehicle, which landed on its roof in the Pacific Ocean, Mendocino County Sheriff Tom Allman said.

Their three other children, including 15-year-old Devonte, are missing.

Devonte, who is black, earned national attention when a photo of him at age 12 went viral. In the image, tears stream down his face as he embraces a white officer in the middle of a demonstration in Portland, Oregon, related to the fatal police shooting of Michael Brown in Ferguson, Missouri. Devonte had been holding a sign offering "Free Hugs."

Investigators, including the Coast Guard, are still looking for the bodies of Devonte and his sisters Hannah, 16, and Sierra, 12. The circumstances of the crash remain unclear.

A welfare check Tuesday at the family's home showed signs that the family's trip was temporary, said Sgt. Brent Waddell of Clark County, Washington. Deputies gained entry to the residence and found pets, as well as conditions that would dictate that their trip was temporary, he said.

The California Highway Patrol received 911 calls Monday about a vehicle that went over the side of Highway 1 in a remote section of Mendocino County, about 180 miles north of San Francisco, Sgt. Erich Paarsch told reporters Wednesday. A passerby noticed the SUV at the bottom of the cliff.

Emergency responders found the vehicle on its roof with the two women, both 38, inside the car, Paarsch said. Outside the car, they found the bodies of Markis Hart, 19, and Jeremiah Hart and Abigail Hart, both 14.

The relatives were not wearing seat belts, Allman said.

The Hart family appears in this undated photo from the Mendocino County Sheriff's Office.

Who were the Harts?

The family had most recently lived in Woodland, Washington.

Child Protective Services had tried to visit the family on Friday, then tried twice more on Monday and Tuesday, to no avail, according to the Washington State Department of Social and Health Services. The agency was trying to get in touch after the "now deceased children were identified as potential victims of alleged abuse or neglect," according to a statement from the Washington State Department of Social and Health Services.

"We have not made any findings in this investigation and we had no prior history with this family. We are working with all involved law enforcement agencies on their respective investigations," the department stated.

Sarah Hart had pleaded guilty to domestic assault, a misdemeanor, involving one of the children in a 2010 incident, in Douglas County, Minnesota, according to court records.

The child had told an elementary school teacher of pain on her back and stomach, which was discovered to be bruises. Hart told police that she had spanked the child over behavioral issues. She was sentenced to community service and one year of probation.

One of the family's neighbors in Washington, Bill Groener, described the children as "wonderful" and said they were home-schooled and kept in the house most of the time.

"I thought it was strange that I didn't see the kids a lot," he told CNN. "The weird thing was that the kids kind of seemed repressed and not communicative."

Family friends had a different perspective on the couple, describing them to CNN affiliate KOIN as loving parents who gave the kids everything they had and radiated positivity.

California trip goes awry

Allman, the sheriff, pleaded with the public for any information about the family's whereabouts.

"We have no evidence and no reason to believe this was an intentional act," Allman said of the wreck. "If this was an intentional act, I truly believe that both between the highway patrol and the sheriff's office, we are going to come to that conclusion. And if we come to that conclusion, you can be assured that that information will be released to the public."

There is every indication that all six children were in the SUV, Allman said, though he said it's possible the three missing children may have been left with friends.

A complicating factor is that investigators don't know when the SUV plunged over the cliff, the sheriff said. The vehicle was in the water for at least several hours before it was discovered, he said, based on the water found inside the SUV and in the wheel well.

The vehicle had to have traveled 75 to 100 feet on a dirt "turn-out" next to the highway before it went off the edge, he said. A turn-out is a place where cars and motor homes can park and people can walk their dogs. There is a dirt berm at the spot but no guardrail.

There were no skid or brake marks, Allman said. It's not clear whether the SUV might have rolled or launched over the edge, said Sgt. Christopher Dalin of the highway patrol.

The viral photo of teen

In the famous photo with Devonte is Portland police Sgt. Bret Barnum, who approached the boy and extended his hand because he saw Devonte crying. The two talked about life, travel and summer vacations before he asked Devonte for a hug, Barnum said at the time.

The Mendocino Sheriff's Office reached out to authorities in Oregon regarding the case, officials said.