A 49-year-old Petaluma man severely disabled in a motorcycle crash remained missing Thursday, more than 24 hours after he was last seen by family members, Petaluma police said.

John Wirth has a severe brain injury that leaves him unable to care for himself and is considered at risk, police said.

A cell phone that he carries but does not use was detected in Vacaville on Wednesday night, but it was unclear how Wirth — who uses a bicycle — might have traveled so far, authorities said.

Wirth left home around 7 a.m. Wednesday on a red Pacific bicycle and was reported missing around 7:30 p.m. when he had not come home.

He is easily confused and unable to manage many normal functions because of traumatic brain injury suffered in the crash, police said.

Wirth is described as a white man standing 6 feet tall and weighing about 180 pounds.

He has a full brown beard and longish brown hair and hazel eyes.

Wirth was wearing a long-sleeved blue shirt with red stripes, a beige baseball cap, black pants and black, green-trimmed shoes.

Anyone with information about his whereabouts is asked to call police at (707) 778-4372.