Leighton Meester and Blake Lively ditch New York's Upper East Side for a downtown party. Plus: Ashlee Simpson, Will Smith and more

FACE TO FACE

After debuting her new single "Little Miss Obsessive" on a Chicago radio station, Ashlee Simpson pokes fun at herself before performing at the Stoli Elite party at the Underground on Thursday. " I love Chicago," Simpson tells PEOPLE. "I want to live here someday."