Tereasa Sue Knuth was 22 when she disappeared from a campsite near Frisco, Colorado, in Summit County. Her boyfriend reported her missing on August 24, 1981, saying she walked away from the campsite and never returned. Investigators found several personal items left behind at the site, including her identification and cigarettes, which prompted questions about whether she left voluntarily.

Tereasa was believed to be wearing blue jeans, a lightweight sweater in pastel pink, green, blue and yellow, and square-toed riding boots. Repeated searches of the rugged terrain by law enforcement and volunteers turned up no trace of her or any belongings. With no witnesses other than her boyfriend and no physical evidence, the case went cold and remains unsolved.

Does anyone who was in the Frisco area around August 24, 1981, or who knew Tereasa, have information that could help investigators?