“Today” show co-host Savannah Guthrie issued a plea for the public’s help on Monday at what she called “an hour of desperation,” as the search for her missing mom, Nancy Guthrie, has entered its second week.

“We believe our mom is still out there,” she said in a video posted to her Instagram account. “We need your help.”

She started the video by saying she wanted to “come on and just share a few thoughts as we enter into another week of this nightmare.”

“I just want to say first of all, thank you so much for all of the prayers and the love that we have felt, my sister and brother and I, and that our mom has felt, because we believe that somehow, some way she is feeling these prayers and that God is lifting her even in this moment and in this darkest place,” Savannah Guthrie said.

“Law enforcement is working tirelessly around the clock trying to bring her home, trying to find her,” she continued. “She was taken and we don’t know where, and we need your help.”

Savannah Guthrie asked, “not just for your prayers, but no matter where you are, even if you’re far from Tucson, if you see anything, if you hear anything, if there’s anything at all that seems strange to you — that you report to law enforcement.”

“We are at an hour of desperation and we need your help,” she added.

The FBI says it is taking two emails seriously, including what appeared to be a ransom note with a second deadline set for Monday. The first deadline was 5 p.m. Thursday, authorities have said. Ransom payment was demanded in bitcoin, but authorities have released few details. 

Authorities had not identified any suspects or persons of interest as of Monday.

An FBI spokesperson told CBS News on Monday evening that “[s]omeone has that one piece of information that can help us bring Nancy home,” and urged anyone with information to call 1-800-CALL-FBI.

The spokesperson said the agency is “not aware of any continued communication between the Guthrie family and suspected kidnappers, nor have we identified a suspect or person of interest in this case at this time.” Agents, analysts and staff have been working on Nancy Guthrie’s disappearance for over a week. Additional personnel continue to deploy to Tucson, and the FBI is currently operating a 24-hour command post, the spokesperson said, adding: “But we still need the public’s help.” 

Savannah Guthrie and her two siblings, Camron and Annie Guthrie, shared a third videotaped plea over the weekend to whoever may have taken their 84-year-old mother from her Tucson, Arizona, home in what the sheriff has called an overnight abduction. Nancy Guthrie was reported missing on Feb. 1. 

“We received your message and we understand,” Savannah Guthrie said Saturday in a short video. “We beg you now to return our mother to us so that we can celebrate with her. This is the only way we will have peace. This is very valuable to us and we will pay.” 

An FBI spokesman said Savannah Guthrie was referring to a message sent to CBS News’ Tucson affiliate, KOLD, on Friday, The Associated Press reported. The television station received a message earlier last week that included the demand for payment.

KOLD said it would not release details about the contents of Friday’s message, citing respect for the family and the investigation. It is still not known if the messages are credible. 

Anyone with possible information on Nancy Guthrie’s disappearance is asked to call 520-882-7463. 

Over the weekend, investigators searched what appeared to be a septic tank in Nancy Guthrie’s backyard. FBI agents on Friday had removed a camera from the roof of Nancy Guthrie’s home and towed a dark-colored SUV from her garage.

CBS News has learned that investigators also canvassed nearby gas stations in an effort to track down any vehicles captured on surveillance cameras around the time Nancy Guthrie went missing.