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.”
“She found ways to touch him all night, and at one point when he was in front of her, she was grinding on his butt,” the onlooker said, adding that “his shirt came unbuttoned, and she started tickling his bare chest playfully.”
When she wasn’t flirting with Rottman, Moore stuck close to her daughter, and stayed until the nightspot closed.
The mother-daughter duo also had an awkward encounter with Kutcher at a CAA/Grey Goose Pre-Golden Globes bash at Soho House Jan. 13. Kutcher arrived at the party after his ex, but the former couple generally avoided any contact.
Willis, however, did spend some cordial, friendly time chatting with him before going back to hanging out with her mom.