Investors bought up shares of Etsy Inc. on Thursday after the online crafts marketplace added to its board of directors a partner of hedge fund Elliott Investment Management L.P., which recently acquired a “sizable” stake in the company. Etsy said Marc Steinberg, who is responsible for public- and private-equity investments at Elliott, has been appointed to the board, effective Feb. 5, and will also join the board’s audit committee. “Etsy has a highly differentiated position in the e-commerce landscape and ...