Earlier this week, authorities said they had yet to identify a person of interest or suspect in the case.
But they said on Friday they were investigating a new message about Nancy Guthrie, potentially related to the investigation.
FBI Special Agent Heith Janke has said the bureau is looking into a potential ransom note sent to several media outlets.
Janke said the note “had facts associated with a deadline with a monetary value they were asking for”, NBC News reported.
A presenter for a local CBS News affiliate told the BBC that her channel had received the “message” but did not detail its contents.
According to news website TMZ, which reportedly received one of the letters, the kidnappers were demanding millions of dollars’ worth of the cryptocurrency, which is popular with criminals and often difficult to trace.
The family has released two previous videos saying they are willing to speak with the potentail kidnapper, and asking to provide proof that her mother was alive.
In a Thursday video, Camron Guthrie – the son of the missing woman – and confirmed that the family had not had any direct contact with kidnappers.
“We have to know that you have our mum,” Camron said in the family’s latest video message. “We want to talk to you.”
The FBI did arrest one individual regarding a fake ransom note on Thursday.
Family, and law enforcement, have warned that Nancy Guthrie may be at risk without her medication.
“She is without any medicine,” Savannah Guthrie said in a previous announcement. “She needs it to survive. She needs it not to suffer.”