Roblox Corp. shares dropped Friday following a report that the social-gaming company’s app in China will be unavailable for an undetermined period after being shut down in December. Roblox RBLX, shares fell as much as 7% in Friday trading and were last down 5% at $84.59. Shares are more than 80% higher than the $45 reference price established when the company went public in March, but nearly 40% lower than their peak close of $134.72 in mid-November. Back in December, Roblox pulled its app for a service separate from Roblox for the Chinese market called “LuoBuLesi,” in partnership with Tencent...