Johan Magnus Thorsteinson (b. March 19, 1905 in Winnipeg, Manitoba - d. August 24, 1948) was a Canadian professional ice hockey right winger who played 4 games in the National Hockey League for the New York Americans in 1932-33.
He played with the Selkirk Fishermen (junior) from 1918 to 1922, including the 1919-20 Memorial Cup Final which they lost. He then moved to the Selkirk Fishermen senior team for two seasons and to the senior Coleman Tigers in 1924-25.
Thorsteinson turned pro in 1925-26 and played minor pro, mostly in western North America, until his retirement in 1935. He got into 4 games for the New York Americans in 1932-33, with no goals or assists.