But the man has been released after questioning, leaving it unclear where the investigation stands into last week's disappearance of Guthrie, the 84-year-old mother of US television news show host Savannah Guthrie.
FBI agents carrying water bottles to beat the heat walked among rocks and desert vegetation at Guthrie's Tucson-area home.
They also fanned out across a neighbourhood about 1.6 kilometres away, knocking on doors and searching through cactuses, bushes and boulders.
Several hundred detectives and agents are now assigned to the investigation, which is expanding in the area, the Pima County Sheriff's Department said.
In a nearby neighbourhood, two investigators emerged from daughter Annie Guthrie's home with a paper grocery sack and a white rubbish bag.
One, still wearing blue protective gloves, also took a stack of mail from the roadside mailbox. They drove away without speaking to reporters.
Barb Dutrow, who was jogging through a neighbourhood where teams were searching, said an FBI agent told her they were looking for anything that might have been tossed from a car.
Dutrow, who was visiting from Louisiana for a convention, said she "can't imagine the feeling of the family of having their mother taken".
A day earlier, authorities said they had stopped a man near the US-Mexico border, just hours after the FBI released videos of a person wearing a gun holster, ski mask and backpack and approaching Nancy Guthrie's home in Tucson.
The man told media outlets early on Wednesday local time he was released after several hours and had nothing to do with Guthrie's disappearance last week.
Authorities have not said what led them to stop the man on Tuesday but confirmed he was released.
The sheriff's department said its deputies and FBI agents also searched a location in Rio Rico, a city south of Tucson where the man lives.
It was the latest twist in an investigation that has gripped the US since Nancy Guthrie disappeared on February 1.
Until Tuesday, it seemed authorities were making little headway in determining what happened to her or finding who was responsible.
The black-and-white images released by the FBI showing a masked person trying to cover a doorbell camera on Guthrie's porch marked the first significant break in the case.
FBI Director Kash Patel said investigators spent days trying to find lost, corrupted or inaccessible images.
More than 4000 calls came into the Pima County sheriff's tip line within the past 24 hours, the department said.
She was last seen at home Janurary 31 and reported missing the next day. DNA tests showed blood on her porch was hers, authorities said.
Savannah Guthrie posted the new surveillance images on social media and said the family believes their mother is still alive.
The longtime NBC Today show host and her two siblings have indicated a willingness to pay a ransom.
It is not known whether ransom notes demanding money with deadlines that have already passed were authentic, and whether the family has had any contact with whoever took Guthrie.
TMZ reported it received a message on Wednesday from someone claiming to know the kidnapper's identity and that they unsuccessfully tried to reach Savannah Guthrie's brother and sister.
The person asked for bitcoin in exchange for the information, TMZ said. The FBI did not immediately respond to a message.
Authorities have said Nancy Guthrie takes several medications and there was concern from the start that she could die without them.
