EVERYONE in the cast of "Gossip Girl" is hooking up with each other - and Chace Crawford and Taylor Momsen are at the center of the latest smooching session. A Page Six spy spotted the co-stars sneak away during their holiday party at Haven on East 51st Street to steal kisses in the corner, but Crawford's rep denies it. We reported last week Ed Westwick and Jessica Szohr were kissing in an airport, and original "GG" couple Blake Lively and Penn Badgley are still going strong.