Zoe Saldana and Bradley Cooper
12/09/2012 at 10:00 AM EST
and Robert De Niro were on hand to celebrate their film Silver Linings Playbook
at the Weinstein Company's special event at the Chateau Marmont in West Hollywood on Friday.
At the candle-lit dinner party, De Niro enjoyed a Purity Vodka martini, while Cooper posed for photos with Zoe Saldana
. De Niro spent part of the night talking with Mel Gibson and Jane Fonda, who were also in attendance.
Diane Keaton was also at the event, but upon arriving, entered the room "looking a bit puzzled," an onlooker tells PEOPLE.
When asked if she was looking for someone, she responded, "No, I'm looking for a drink," the source adds.
– Kristin Boehm