Dozens of celebrities packed the Belasco Theater in Los Angeles on Tuesday night to celebrate ESPN Magazine’s Body Issue, which features Patriot Rob Gronkowski in the buff on the cover. Guests besides Gronk, who seemed rather pleased with the results of his photo shoot, included former “House” actor Jesse Spencer , whose surfer girlfriend, Maya Gabeira, is also featured in the magazine; former New England Patriot Jim Plunkett ; and actor Edi Gathegi , of “Twilight” and the Boston film “Gone Baby Gone.”