The 24-year-old Gossip Girl actor showed off his muscles the day before in a sleeveless shirt while attending the first day of the annual concert weekend.
Penn was joined both days by his Easy A co-star Dan Byrd and Desperate Housewives actor Shawn Pyfrom.
Penn’s Gossip Girl co-star Taylor Momsen recently said how she is grateful to the show for writing her out of scenes so she can tour with her band The Pretty Reckless.
