Watch: The Truth Behind Our Obsession With True Crime Stories. Authorities are trying to locate Slack cofounder Stewart Butterfield’s 16-year-old child. Mint Butterfield was last seen late April 21 in Bolinas, Calif., a Marin County Sheriff’s Office deputy said in a statement posted on the department’s Nextdoor account April 23. The police added that the teen is approximately 5’0″ tall and weighs 100 pounds, has reddish brown curly hair and pierced eyebrows and was last seen wearing a black sweatshirt, flannel pajama pants, and black boots.