Correction: The original report stated that Ryan was retired, which was incorrect. Ryan was currently teaching at Logan at the time of his disappearance.
San Mateo County sheriff's deputies are searching for a James Logan High School teacher who was last seen Tuesday morning.
Christopher Ryan, a 54-year-old Redwood City resident, is considered at-risk because he needs daily medication for a medical condition.
Ryan's sister, Katie Glapzel, reported him missing after she had not heard from him in more than 24 hours, according to the San Mateo County Sheriff's Office.
Ryan was last seen around 8:20 a.m. on Tuesday in Redwood City, where he lives.
His car was found Wednesday just after 11:30 p.m. off the side of the road near the junction of highways 280 and 92 in San Mateo County.
His cell phone and medication were in the vehicle.
Glapzel told deputies it is very unusual for Ryan not to keep in contact with his family.
Several of Ryan's former students have begun circulating a Missing Person's flyer online and have commented that he taught at the Union City high school on Redwood City Patch's original report of his disappearance.
Glenn Nate, a student of his in 2005, said he taught world literature at Logan and described him as, "One of the most intelligent and inspirational people I know."
Ryan is a white male, 54 years old, approximately 6 feet tall and weighs around 170 pounds. He has blond hair, blue eyes and a medium complexion.
If you have any information on Ryan or believe you have seen him, please contact Detective Armando with the San Mateo County Sheriff's Office at 650-363-4911.