The daughter of Slack co-founder Stewart Butterfield and Flickr co-founder Caterina Fake, Mint Butterfield, has disappeared without a trace in the United States. She recently turned 16. Posters urging help in the search for the girl are plastered on the streets of San Francisco, reports Daily Mail. Details Four days ago, Mint disappeared from her mother’s house in the affluent Marin County, California. Police do not rule out that the teenager may be in the center of San Francisco – Tenderloin, the city’s most crime-ridden district, known as the “heroin ghetto.” Nearby are City Hall, the Conser…