The search for Nancy Guthrie, the 84-year-old mother of NBC’s Today show anchor Savannah Guthrie entered its sixth day on Friday in Arizona, as authorities said they believe that she is still alive.

“She’s out there, we’re gonna find her, we have to,” said Chris Nanos, Arizona’s Pima county sheriff, in an interview with ABC’s Good Morning America show on Friday morning. “Pray – just pray,” he said.

Asked by the interviewer if he could “work on prayers” in the absence of good leads in the case or a means of contacting those believed to have abducted Nancy Guthrie, Nanos added: “Sometimes I have to, I do not have a choice.”

The Federal Bureau of Investigation (FBI) is offering a $50,000 reward for information that leads to Guthrie’s recovery and/or the arrest or conviction of anyone involved in her mysterious vanishing.

Nancy Guthrie was reported missing on Sunday morning in the Tucson area after she failed to show up to her regular church. She was last seen by loved ones at her home in the Catalina foothills neighborhood to the north of the southern Arizona city on the evening of 31 January.

Her disappearance is being investigated as a possible kidnapping, and as of Friday morning, no suspect or person of interest had yet been identified.

On Thursday night, Savannah’s brother, Camron Guthrie, issued a new plea in a video posted on social media.

“Whoever is out there holding our mother, we want to hear from you,” he said. “We haven’t heard anything directly. We need you to reach out, we need a way to communicate with you so we can move forward. But first, we have to know you have our mom. We want to talk to you and we are waiting for contact.”

The appeal came shortly after Nanos held a press conference where he said that authorities believe that Guthrie is still alive.

“Right now, we believe Nancy is still out there” Nanos said. “We want her home. Our department – the sheriff’s department – along with all of our partners at the FBI, have been working around the clock, and we just want her home and to find a way to get to the bottom of all of this, just as you do.”

Nanos confirmed that spatters of blood found near the front door of Nancy Guthrie’s house had tested positive for her DNA. He also said that Guthrie’s pacemaker had disconnected from her personal monitoring device at 2.28am Sunday. Authorities have also said that her doorbell camera was disconnected the night she disappeared.

The FBI is offering a $50,000 reward for information that leads to Guthrie’s recovery and or the arrest or conviction of anyone involved in her disappearance.

“She is considered to be a vulnerable adult who has difficulty walking, has a pacemaker, and needs daily medication for a heart condition,” the FBI’s missing person bulletin states.