UPDATE: A day into Chipotle's contest on Roblox, users had trouble accessing the Roblox platform, Chipotle tweeted Friday. Roblox said at 6:36 p.m. ET Friday that it was making progress on the outage.

At its annual developer conference Thursday, Roblox painted a picture of what’s next for the fast-growing online multiplayer portal that’s like catnip for kids and teens. In his keynote, Roblox ...