TikTok Chief Executive Officer Shou Chew said that V. Pappas, the social media giant’s chief operating officer, is stepping down to focus on “entrepreneurial passions.” Adam Presser, the company’s chief of staff, will become head of operations. Zenia Mucha, former head of communications at Walt Disney Co., is joining as chief brand and communications officer, a new position. Pappas has been the longtime public face for TikTok in the U.S.