Cyril Willard Thistle, known as Sonny, was 26 when he vanished from Brampton, Ontario in the winter of 1981. Family members last saw him near McLaughlin Road and Queen Street East. At the time he was described as fair complected, with light brown hair, a thick moustache and a noticeable gap between his two front teeth. He identified as Indigenous and was living a transient lifestyle, moving between Toronto and the Region of Peel; before 1980 he had lived in Saskatchewan and Sudbury.

A handwritten letter linked to Cyril is dated April 1981, but no formal missing person report was filed until August 2013, more than thirty years after his last known contact. Peel Regional Police describe their inquiry as exhaustive and the investigation remains open; an age-progressed composite was released in September 2022 to try to generate leads. Very little is publicly known about what happened after that last sighting.

If anyone knew Cyril, saw him in Brampton or the Toronto area in 1981, or has information that could help locate him, please come forward.