CMG Communications LLC is moving from 79 Fifth Ave. to 257 Park Ave. South after leasing the entire 11,513-square-foot 13th floor. Eric Derfner of the Feil Organization represented the landlord, 257 Park Ave. Associates. Greg Taubin and David Goldstein of Julian J. Studley Inc. represented CMG Communications. CMG Communications is a New York based advertising agency. Known as the Gramercy Park Building, 257 Park Ave. South contains 230,000 square feet of rentable area on 20 floors. It is currently 98 percent leased and is famous for its intricate gargoyles and Art Deco graphics.