Katy Perry Celebrates Her Brother's Birthday – Without John Mayer
08/14/2012 AT 06:00 AM EDT
Hanging with her friend Markus Molinari and her stylist, Johnny Wujek, Perry "seemed very happy and she was really having fun," an onlooker tells PEOPLE.
Also unwinding at Bootsy Bellows Friday: Leonardo DiCaprio and pal Lukas Haas; venue owner David Arquette; and Glee's Naya Rivera, Chord Overstreet and Kevin McHale.
– Jennifer Garcia