“When a vegan goes missing do they put them on a soymilk carton?”

Missing persons’ pictures have been on milk cartons since the disappearance of Etan Patz in Manhattan in 1979. “Must suck when a vegan’s kid goes missing and his picture is put on a carton of normal milk” is a joke that was cited on Twitter on April 9, 2012.
 
“When a vegan goes missing they put them on a soymilk carton” was cited on Twitter on May 12, 2012.
 
   
Wikipedia: Disappearance of Etan Patz
Etan Kalil Patz (/ˈeɪtɑːn ˈpeɪts/; October 9, 1972 - declared legally dead in 2001) was an American child who was six years old when he disappeared in Lower Manhattan, New York City, on May 25, 1979. He is the best known missing child from New York City. His disappearance helped spark the missing children’s movement, including new legislation and various methods for tracking down missing children, such as the milk-carton campaigns of the mid-1980s. Etan was the first ever missing child to be pictured on the side of a milk carton.
 
Twitter
Sam LW
‏@DoubleBerg426
Must suck when a vegan’s kid goes missing and his picture is put on a carton of normal milk.
10:47 PM - 9 Apr 2012
 
Twitter
Creepy Van Ewen
‏@VaguelyFunnyDan
When a vegan goes missing they put them on a soymilk carton.
2:10 AM - 20 May 2012
 
Twitter
Funny One Liners
‏@funnyoneliners
When a vegan goes missing they put them on a soymilk carton.
RT @VaguelyFunnyDan
8:03 PM - 7 Aug 2012
 
Google Books
More One Liners, Jokes and Gags
By Grant Tucker
London: The Robson Press
2013
Pg. ?:
When a vegan goes missing they put them on a soyamilk carton.
   
Google Books
Roadmap into a Twisted Mind
By Bruno Gagnon
Victoria, BC: FriesenPress
2014
Pg. 57:
When a vegan goes missing, they put them on a soymilk carton?