UPDATE: The boy had been found safe in an Alameda County medical facility by Monday afternoon, San Francisco police said. No foul play is suspected.

San Francisco police are asking for help finding a 13-year-old boy considered at-risk.

Knowledge Shepard was reported missing on Friday. He was last seen entering the Embarcadero BART station at 7 p.m. that day.

Shepard has a fascination with buses and trains and usually rides MUNI or BART, police said. He is described as 5-feet-5-inches tall, weighing 98 pounds, with a bald head and brown eyes. He is considered at-risk due to a preexisting medical condition.

He was last seen wearing a black Nike hoodie sweatshirt with sleeves ripped off, a burgundy harness, gray khaki pants and white shoes with blue and orange checkmarks.

Authorities urge anyone who locates Shepard to call 911 and report his current location and physical description.

The San Francisco Police Department urges anyone with information on his possible whereabouts to call its tip line at 415-575-4444 or text TIP411 and begin the message with "SFPD." Tips can be submitted anonymously.