HALLS, Tenn. — UPDATE 11 A.M. MONDAY: The Knox County Sheriff's Office is asking the public in the Halls area to search barns, outbuildings, creeks and any empty vehicles on their property for the possible whereabouts of a man with dementia now missing eight days.

Jack Harrison, 77, was last seen about 9 p.m. Sunday, Nov. 17, at the Walmart in Halls. He became separated from family members.

Video from the store shows him at the Walmart gas pumps parking lot, heading toward Norris Freeway, according to the Sheriff's Office.

Sheriff Tom Spangler also wants residents to check with other residents and compare notes in case one may have seen something significant. Some people may not have paid attention to news reports about Harrison, and there's a chance they've seen something that may be important regarding Harrison's disappearance.

It's also possible residents with surveillance cameras in the area may have captured footage of Harrison.

If possible, those with cameras should go back to the night of Nov. 17, in case Harrison was recorded nearby.

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.

If you spot Harrison, call 911 promptly. Anyone with possible information about his whereabouts is asked to call detectives at 865-215-2243.

PREVIOUS STORY: Nearly a full week has passed since 77-year-old Jack Harrison was separated from his family at the Halls Walmart, but law enforcement and volunteers are not giving up their search efforts to find him. 

"My dad has disappeared for hours before, but he's never been gone this long," said Jackie Taylor, Harrison's daughter. "It's Thanksgiving on Thursday, as you guys know; we cannot have Thanksgiving without our dad. He's probably very confused. It's been raining and cold; we just need him home."

Harrison disappeared the night of Sunday, Nov. 17 and a Silver Alert was issued Thursday evening. The Knox County Sheriff's Office said he suffers from dementia and other severe medical conditions that require medication.

RELATED: SILVER Alert issued for 77-year-old man with dementia last seen at Walmart in Halls Sunday night

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. 

Since his disappearance, crews have been canvasing neighborhoods and scouring every corner of the area in hopes of finding him.

"We've been together 37 years, and he's a great father and husband and everything," his wife Karen Harrison told 10News. "We're really, really worried about him."

Karen, Jackie and other relatives held a prayer vigil for Harrison's safe return Saturday evening. Volunteers who have been aiding in the search gathered too.

"He's a great guy. We love him," his daughter Jackie Taylor said. "We have to bring him home; he needs to be found now."

On Friday, deputies with KCSO's tracking team searched all day, including along Beaver Creek. No sign of him has been discovered yet.

Volunteers joined in the search, walking around the area where he disappeared and calling his name.

Family members told them to say "Jack, Karen's waiting for you," if they found him in order to keep him in one location. Karen is the name of Jack's wife.

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.