Savannah Guthrie's brother, Camron Guthrie, has pleaded with those who are suspected of abducting their mother, Nancy Guthrie, to "reach out".
According to authorities in Pima County, Arizona, the 84-year-old was last seen at her home on Saturday evening.
Police investigators believe Nancy was taken "against her will" from the property in the middle of the night.
In a new video posted to Instagram on Thursday, retired fighter pilot Camron begged those responsible for his mother's disappearance to make contact with authorities.
"This is Camron Guthrie. I'm speaking for the Guthrie family," he stated. "Whoever is out there holding our mother, we want to hear from you. We haven't heard anything directly. We need you to reach out, and we need a way to communicate with you so we can move forward. But first, we have to know that you have our mom. We want to talk to you, and we are waiting for contact."
On Wednesday, Today show co-anchor Savannah was joined by Camron and their sister, Annie Guthrie, for an emotional video in which they addressed media reports regarding an alleged ransom letter.
The letter, which has not been verified, demands a substantial amount of Bitcoin.
"We too have heard the reports about a ransom letter in the media. As a family, we are doing everything that we can. We are ready to talk," the 54-year-old commented. "However, we live in a world where voices and images are easily manipulated. We need to know, without a doubt, that she is alive and that you have her. We want to hear from you, and we are ready to listen. Please, reach out to us."
Earlier on Thursday, Federal Bureau of Investigation (FBI) detectives announced a $50,000 (£37,000) reward for information that leads to the discovery of Nancy.
"The FBI is now working this case jointly with the Pima County Sheriff's Department, and we're going to start today by announcing a $50,000 reward for information leading to the recovery of Nancy Guthrie and or the arrest and conviction of anyone involved in her disappearance," said Heith Janke, Special Agent in Charge of FBI Phoenix, at a press conference.
