Courtney Cox and Chelsea Handler were among the gaggle that joined Aniston and Theroux at the Chateau Marmont Thursday night to bask in the afterglow of the premier.
"Everyone seemed to be getting along and in a celebratory mood," said the source.
A spectator at the night spot added that the couple seemed to be in a giddy and fairly romantic state with Aniston wearing Theroux's jacket over her Balenciaga dress.
"They were super cute," the witness said. "He had his arm around her and kissed her on her cheek."