The search for Nancy Guthrie has suffered another setback after a hair found at the scene of her disappearance yielded no new DNA evidence.

Guthrie, the 84 year-old mother of NBC News host Savannah Guthrie, disappeared from her home in the Catalina Foothills suburb of Tucson, Arizona, on February 1, with this Saturday marking the six month anniversary.

Speaking to Fox News Digital as the milestone looms, Pima County Sheriff Chris Nanos admitted that hopes had been raised by the discovery of the hair, only to be dashed.

“Yes, there was a hair,” he said. “We had it and thought, ‘OK, well, we’ll do the DNA first,’ right? You’re going to do DNA before something else.”

Nanos’s department, which has been working with investigators from the FBI, sent the sample on to a specialist laboratory in California for analysis.

“It came back... there’s no DNA,” he explained. “But does that mean the hair isn’t that of the suspect? We won’t know that till we have the suspect’s hair. You don’t just destroy it.

“There’s other things that hair may prove valuable for, but right now it was just about, ‘Is there any DNA there?’ And the answer was no. That was just a matter of weeks ago.”

The sheriff concluded: “Anything we can grasp onto with DNA is a part of this investigation. That’s really where some of my optimism is, that I just know that we’re gonna get this thing resolved.

“We believe, just as the family does, just as Savannah does, somebody knows something. We need that person to call us.”

Taking to Instagram this week, Savannah Guthrie issued a fresh appeal to her mother’s abductor to free her.

“It has been months since our mom was taken from us,” she said. “Our family is in agony. We are in a nightmare that will not end. Nothing about our situation has changed.

“We have done our part. We will never stop looking for her. We will always ache for her, feel that hole in our hearts.”

Guthrie continued: “The world can be a cruel and unforgiving place, and I know that you have tried to do things the right way. So I’m asking you, begging you to do the right thing now. Make the right choice.

“Help us find her. Tell us where to look for her. I truly believe it is never too late to do the right thing. Help us bring this situation to an end.”

Investigators have said they believe Nancy was taken against her will after finding blood near the entrance to her home.

The FBI later released surveillance footage from the victim’s Nest doorbell camera showing a masked individual wearing gloves and a black Ozark Trail backpack near the property around the time she disappeared.

The case has drawn a massive search effort involving law enforcement officers, volunteers and search teams who have combed desert areas surrounding Tucson and beyond. Despite their extensive efforts, Nancy has not been found.

It was reported last month that police had received a ransom note, seemingly from Nancy’s abductor, claiming she had died.

However, the authorities have not publicly confirmed the note’s authenticity nor provided details about precisely what it said.