"She keeps herself grounded," Liam told Access Hollywood when asked about Jennifer at the junket for his latest movie, "Paranoia."
"She bounces off walls every time she comes into a room and she's such a great person," the 23-year-old actor continued. "Working with her is so much fun".
In the upcoming "Catching Fire," the events for Katniss, Peeta and Gale get very grim, but Liam said Jennifer's amazing (and often goofball) personality kept the cast and crew's spirits lifted.
"We have a lot of kind of dark subject matter in 'The Hunger Games,'" he said. "She just comes to set with so much life and it's so contagious, and she's so much fun to be around."
Adding, "She's a great friend now."
"Paranoia" hits theaters on August 16 and "The Hunger Games: Catching Fire" opens on November 22.