Davey Johnson texted a photo to a friend and said he was headed home to Sacramento

A well-known US automobile journalist has not been seen for almost a week since taking a motorcycle for a test-drive in mountainous northern California, police and industry media said.

Davey Johnson, 44, from Sacramento, was testing a Honda CB1000R in the rugged and cold terrain for an article in Motorcyclist magazine.

But the bike was found at the weekend at a rest stop on Route 49, near Mokelumne Hill town, with helmet and folded gloves, according to police and the magazine Car and Driver.

Police also found Johnson's clothes, phone, laptop and wallet, neatly placed by a snow-fed creek nearby.

His last-known communication was a June 5 text to his girlfriend, multiple media outlets said. He had also texted a photo to a friend and said he was headed home to Sacramento, about 65 miles from his bike and possessions.

Teams of policemen and volunteers, along with six search dogs and a helicopter, have been searching river banks and the highway since Saturday, his friends said on social media.

In different interviews, his girlfriend Jaclyn Trop said she was not giving up hope and believed he could survive if lost.

"I just hope he's figured out how to stay alive," she told Car and Driver at on Saturday.