The Pima County Sheriff's Department has handled some 18,000 tipster calls about the disappearance of Nancy Guthrie from her Tucson home, the agency said.
Even more leads have been submitted to the FBI, which has its own tip line.
The Sheriff's Department said Wednesday that it continues to follow leads in the case.
It said more than 4,000 tips were called into the department in the last 24 hours.
The county's anonymous tip line — 88-CRIME — has collected more than 1,000 tips in connection with the Guthrie case, said Pima County Attorney Laura Conover.
Investigators were seen Wednesday searching the desert around Guthrie's Catalina Foothills home.
"Several hundred detectives and agents are currently assigned to this case, and you will continue to see increased law enforcement activity throughout Pima County as the investigation expands," an update Wednesday from the Sheriff's Department said. It said investigators assigned to the case are working around the clock.
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On Tuesday, a Rio Rico man was detained and questioned in the case before being released.
In Wednesday's update, the department simply noted: "One adult male detained Tuesday afternoon for questioning has been released after speaking with investigators. This detention was part of follow-up on incoming leads. As with any investigation, we do not release the identities of individuals who are detained and later released without charges."
Anyone with "actionable information" is asked to contact 1-800-CALL-FBI or the Pima County Sheriff's Department non-emergency line at 520-351-4900.
Nancy Guthrie — the mother of “Today” show host Savannah Guthrie — disappeared on Feb. 1.
