Nancy Guthrie's whereabouts remain a mystery four months after vanishing

Savannah Guthrie and her mother Nancy, who was last seen on January 31. (Instagram)

For more than a decade, Savannah Guthrie has beamed into living rooms of Americans as the co-anchor of NBC's TODAY show, one of the highest-rating morning television programs in the country.

So when her mother Nancy Guthrie went missing in January, her fame sparked a national obsession with the case and grabbed headlines around the world.

Savannah Guthrie is a well-known media personality in the US. (AP: File)

Despite the publicity and hundreds of sheriff's deputies, FBI agents and volunteers searching for the 84-year-old, Nancy Guthrie has still not been found.

It has been four months since she disappeared and just under that since the release of eerie doorbell footage showing a masked person at her door.

This is a timeline of events leading up to her alleged abduction and key moments from throughout the case.

The community has thrown its support behind the search for Nancy Guthrie. (Reuters: Rebecca Noble)

5:32pm: Nancy Guthrie takes an Uber to her daughter Annie's home for dinner and a games night.

9:48pm: She is driven home by her son-in-law, Tommaso Cioni.

Mr Cioni watched from his car as Ms Guthrie walked to her garage and safely entered her house in the Catalina Foothills neighbourhood of Tucson, Arizona, police told The New York Times.

The home of Nancy Guthrie in Tucson, Arizona. (AP: Caitlin O'Hara)

1:47am: The doorbell camera at Ms Guthrie's home is disconnected.

Investigators initially said there was no video available because Ms Guthrie did not have an active monitoring subscription.

But digital forensics experts kept working to find images in back-end software that might have been lost, corrupted or inaccessible.

2:28am: Ms Guthrie's pacemaker app disconnects from her phone.

The timeline of the hours leading up to Nancy Guthrie's disappearance released by local authorities. (ABC News Graphics: Lindsay Dunbar)

11:56am: Her family checks on her after learning she did not attend church. Moments later, they call 911 to report her missing.

12:15pm: Investigators arrive and launch a search operation, including the use of drones and dogs.

The Pima County Sheriff's Department holds its first news conference, announcing the investigation.

Sheriff Chris Nanos said he believed Ms Guthrie had been abducted and declared her home a crime scene.

"This is not dementia-related. She's as sharp as a tack," he said.

"The family wants everyone to know that this isn't someone who just wandered off."

Sheriff Nanos raised concern that Ms Guthrie was reliant o