Duvall was last known to be in the Manitowoc, Wisconsin area in the autumn of 1988. Her ex-husband reported her missing on October 1 of that year. She has never been heard from again. Duvall's ex-husband stated she was a good mother and it was uncharacteristic of her to abandon her two sons willingly. He had custody of the children, but they usually visited their mother on weekends. Duvall's ex-husband said he had maintained a friendly relationship with her since their divorce four years prior to her disappearance.

Investigators renewed their search for Duvall in 2007. She was living on a dairy farm on South Parkview Road with John Neuser at the time of her disappearance and he continued to reside at the home for over a decade afterward, moving away in 2006. Authorities searched Neuser's former property for evidence in Duvall's case in January 2007. He is described as a person of interest in Duvall's case, not a suspect, and has not been charged in connection with it.

Duvall's Social Security number has not been used since 1988, and she has not had contact with law enforcement in the United States since she went missing. Her disappearance remains unsolved.