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 got into an argument with her boyfriend, stepped out for a breath of fresh air and never returned. She has never been heard from again. Her mother does not believe Sjoberg 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 a dating couple, both nineteen years old, were found in a wooded area a month after they vanished from the parking lot of Concord House after a wedding reception. Due to the similarities, there was some speculation that their murders and Sjoberg's disappearance were connected. In 2009, DNA evidence lead to the arrest of a suspect, Edward "Wayne" Edwards, in the double murder. He near the Concord House in 1980 and worked there as a handyman. He has a substantial criminal record dating back to 1955 and was once on the Federal Bureau of Investigation's Ten Most Wanted list. Authorities don't believe Edwards was involved in Sjoberg's disappearance, however, as he wasn't even in the state of Wisconsin when she went missing.

Sjoberg's mother held a memorial service for her in 1995, twenty-one years after her disappearance. Her case remains unsolved.