Katy Perry has been out partying with pals following her divorce.

The singer and her husband Russell Brand announced their split in December last year.

Although Katy and Russell vowed to remain on good terms, it appears their relationship has turned sour since they signed divorce papers on February 8.

Katy is said to be shocked by rumours that Russell, 36, is now dating a woman he met at a yoga class.

In spite of her heartbreak, Katy was seen out frolicking with chums deep into the wee hours of Thursday morning.

"Katy was partying with a bunch of pals at the Spare Room at the Roosevelt Hotel in LA," an eyewitness told Life & Style. "She came in around 1:30 a.m. She was wearing a gray sweatshirt and sweatpants with blue high pumps."

Katy was accompanied by a number of cute companions.

"She was also with a bunch of male friends, and they played numerous games of bowling," the eyewitness continued. "They were drinking mixed vodka drinks and having a blast!"

Katy was in great spirits and seemed enlivened by hanging out with her friends.

"It was obvious that she liked being out and having a fun, carefree time, without crowds of people around her. She was all laughs and smiles with her friends," the source detailed. "Security left at 2:15 a.m., but Katy stayed behind with her pals and continued the party."

Katy's new single Part of Me, which is rumoured to be written about her relationship challenges with Russell, has reached number one on the US Billboard Hot 100 charts.