06/26/2012 AT 6:00 AM ET
Popping into Beacher’s Madhouse inside the Hollywood Roosevelt Hotel at around 11:45 p.m., the “Can’t Be Tamed” singer was joined by a group of girlfriends – and they immediately headed to Cyrus’s usual table in the front row of the club.
“Miley spent most of the night dancing,” an onlooker tells PEOPLE, adding that she shimmied to songs by Pitbull and Michael Jackson.
But it wasn’t until Rihanna came on that Cyrus really seemed to be having a ball on the dance floor.
“She threw her hands in the air when the deejay started playing, ‘We Found Love,’ ” the source says. “She was very chatty and was in a great mood. At around 12:15 a.m., she pulled her girlfriend into the photo booth to take pictures together.”
Also on hand that evening was Alexander Skarsgard.
The True Blood hunk was “approached by a handful of girls,” says the source, but “[seemed to enjoy] his evening mostly under the radar.”