The FBI has acknowledged a "new message" tied to the disappearance of Savannah Guthrie's mother Nancy.

The Today show presenter Savannah's mother Nancy vanished from her home in Arizona last week, prompting an investigation by officials at the Federal Bureau of Investigation's Phoenix Field Office and the Pima County Sheriff's Department.

In a new update, the Pima County Sheriff's Department said in a statement to PEOPLE: "The FBI and Pima County Sheriff's Department are aware of a new message regarding Nancy Guthrie.

"Investigators are actively inspecting the information provided in the message for its authenticity. While this is one new piece of information, the FBI and the Pima County Sheriff's Department are still asking anyone with tips to contact the FBI at 1-800-CALL-FBI. The FBI continues to offer a reward of up to $50,000 for information leading to the recovery of Nancy Guthrie and/or the arrest and conviction of anyone involved in her disappearance."

This comes after the sheriff investigating Nancy's disappearance said people "have to have hope".

Pima Count Sheriff Chris Nanos has been at the forefront of the ongoing investigation and he struggled to hold back his emotions during a televised interview this week.

Speaking to NBC's Liz Kreutz, Nanos was asked why he believes she is "still out there" despite naming no suspects or persons of interest.

With his voice trembling, he said: "You have to have hope. You have to have hope.

"Come on, this is somebody's mom. We're gonna find her."

Authorities previously confirmed they are investigating a ransom note demanding bitcoin which was shared with media.

A separate fake ransom note has led to an arrest, and FBI Agent Heith Janek insisted it came from "someone that was trying to profit from [Nancy's case], a total imposter".

He added: "My next message is to those imposters who are trying to take advantage and profit from this situation.

"We will investigate and ensure you are held accountable for your actions."

The FBI has offered a hefty sum in exchange for information that leads to her safe return or the apprehension of anyone involved in her disappearance.

Special Agent Janke said: "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."

Savannah and her siblings Annie and Camron have been appealing to the abductor to get in touch to let them know she is alive.

The presenter said in a video alongside her siblings: "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.

"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."

She added of Nancy: "She is 84 years old. Her health, her heart is fragile. She lives in constant pain. She is without any medicine. She needs it to survive. She needs it not to suffer."