updated 01/24/2012 AT 8:50 PM ET
•originally published 01/25/2012 AT 8:45 AM ET
Wearing a short black skirt and striped sweater, the actress, 49, arrived at Beacher’s Madhouse at The Roosevelt Hotel just after 11 p.m. on Jan. 11.
“When she first arrived, she kept to herself … but she started loosening up and getting into party mode,” an onlooker tells PEOPLE about Moore, who sipped Red Bull at the hot spot. “She seemed really happy to be out with her daughter’s friends.”