'We are ready to talk' - US news anchor Savannah Guthrie addresses mother's abductor

US news anchor Savannah Guthrie and her siblings have posted an emotional video where they address whoever could have abducted their mother.

"We are ready to talk," the NBC presenter says in the video posted to Instagram. "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."

The clip comes amid a search for 84-year-old Nancy Guthrie, who went missing in the middle of the night over the weekend.

Authorities in Arizona have said they received a copy of a possible ransom note and were working with the FBI to authenticate it.

The Today show host, flanked by her sister Annie and brother Cameron, was emotional and teared up several times throughout the video posted on Wednesday night.

"Mommy, if you are hearing this, you are a strong woman," she said, her voice breaking.

"Everyone is looking for you, mommy. Everywhere. We will not rest. Your children will not rest until we are together again."

Investigators in Arizona, where Nancy went missing, said they have not yet identified a suspect and have pleaded for the public's help.

Pima County Sheriff Chris Nanos has described an all-hands-on-deck search that has included dogs, drones, helicopters and the FBI.