Sjoberg was last seen leaving her Oconomowoc High School prom during the early morning hours of June 5, 1974. The prom was held at the Concord House dance hall, on an Interstate 94 interchange in Concord, Wisconsin. Sjoberg stepped out for a breath of fresh air and never returned.

Sjoberg has never been heard from again. Her mother does not believe she ran away; she was scheduled to distribute programs at the Oconomowoc High School commencement the day after her disappearance and was going to serve as the maid of honor at a family wedding, and it would be unlike her to miss these events. She is described as a happy teenager who had no problems and no reason to leave.

Six years after Sjoberg's disappearance, the bodies of two Fort Atkinson High School students were found in a wooded area a few months after they vanished from the parking lot of Concord House. Their slayings remain unsolved. Sjoberg's mother believes the murders and Sjoberg's apparent abduction may have been committed by the same person, but there is no evidence to support any theory. Her mother held a memorial service for her in 1995, twenty-one years after her disappearance. Sjoberg's case remains unsolved.