“Family Guy” creator Seth MacFarlane’s wild birthday bash in LA on Saturday had a 1950s New York theme, as well as gambling tables, dancing women in a box with red lights and acrobats climbing the walls. Disney star Demi Lovato, 19, shocked guests when she arrived holding hands with on-again, off-again boyfriend Wilmer Valderrama, 31, although she’s insisted they are not a couple. “They were dancing and making out all night,” a spy told us. “She was doting on him.” Meanwhile, “House” star Olivia Wilde hit the dance floor with Edi Gathegi. Spies say Mel Gibson kept to himself while tech mogul Sean Parker was bombarded with A-list admirers.