The Knox County Sheriff's Office has issued a SILVER Alert Thursday and is pleading for public help in finding a missing elderly man who suffers from dementia and other severe medical conditions.

According to the KCSO, 77-year-old Jackie Harrison was separated from his family at the Halls Walmart and is feared to have walked off on the evening of Sunday, Nov. 17.

Sheriff Tom Spangler said he has several medical conditions which require medication.

He was last seen wearing blue jeans, a polo shirt, tennis shoes, brown jacket and a ball hat with a Broncos emblem on the front.

On Tuesday, KCSO said deputies were out canvassing the Halls area to find him. They also released a new photo of Harrison:

Jackie Harrison
Jackie Harrison
KCSO

On Wednesday, a small group of volunteers joined the search, walking around the area where he disappeared and calling his name.

RELATED: Volunteers join search for missing elderly man in Halls

The Knox County Sheriff's office devoted 26 members of the Special Operations Response Team (SORT) on Thursday, with patrol officers joining them between other calls. 

"Sheriff Tom Spangler is asking the public to remain vigilant, if you see someone who matches the description of Mr. Harrison please call 911. If at all possible try to keep him in your sight until one of our Officers can arrive, if you feel comfortable you may approach him and talk to him," according to a release.

Anyone who sees him or has information about his whereabouts should call 911 or the Knox County Sheriff’s Office at 865-215-2243.