"This case continues to be investigated as a kidnapping for ransom case," the FBI said in a statement.
The man allegedly used an app to create a fake phone number to text the family, according to a federal complaint.
The "Today" show host and her siblings made an emotional plea for the return of their mother, who remains missing in Arizona.
Investigations are continuing after the mother of "Today" show host Savannah Guthrie disappeared over the weekend in what authorities believe was a possible abduction.
The FBI has seized a website that a notorious ransomware gang, which has extorted more than $100 million from victim organizations, has used to shame its victims, according to a posting on the website.
Thieves stole thousands of dollars from a couple's bank accounts through Zelle.
