Savannah Guthrie has posted multiple videos on social media making direct appeals to her mother’s captor, and is offering $1m (£760,000) for information that leads to her return.
“She may be lost, she may already be gone,” Savannah said in a video shared in February.
There have been arrests and detainments in the case, but they have not led officials to find the actual suspect.
A California man arrested on suspicion of sending fake ransom notes is facing federal charges, but does not seem to be involved in Nancy’s disappearance.
A delivery man was also detained for questioning, but he was released shortly after he was cleared by authorities.
So far, the lone glimpse officials have of the suspect is of a masked man whose image was captured on the doorbell camera outside Nancy Guthrie’s home.