Britney Spears Parties with Tony Romo
The pop star, dressed in a masquerade ball mask, and Sims, first made a quick stop at the L.A. restaurant Ketchup where Romo was having dinner.
"[Spears] walked around the restaurant into the lounge where she met up with some people," an observer tells PEOPLE. "She didn't eat or drink ...[It] seemed like she was rounding up people to go [out]. She was very friendly and smiley, in and out."
Another source says, "Alli was meeting up with Tony and his friends at Ketchup and Britney wanted to come along. Tony and Alli have been good friends. They've known each other for a little over a year. "
Later, Romo met up with Sims, Spears and other pals at the Hollywood hotspot Les Deux where they hung out for a friendly low-key night upstairs.
Spears was "sitting with her friends and Tony. Everyone was just hanging out. Brit was upbeat, really seemed fine."
The following night, perhaps in a nod to her friend Romo, a source says "Sims even playfully dressed as a quarterback for Ryan Cabrera's costume party on Saturday night."