In a big show of support for the actor's J/P Haitian Relief Organization, celebrities including Gwyneth Paltrow and Chris Martin, Julia Roberts and Danny Moder and Kevin Bacon walked the red carpet on Saturday, mingling with each other and sharing a few laughs, before moving on to a cocktail hour inside the Montage Hotel.
"This town has been very supportive of me and, more importantly, what our organization is doing in Haiti," Penn told PEOPLE. "I got a lot of gratitude and no complaints."
But it's a two-way street, Michael Douglas, who attended the event solo, told PEOPLE.
"I'm impressed with what he's done with the Haitian relief. He's not afraid to learn and be vulnerable," said the actor, who recently returned from a Christmas vacation with his family in Quebec.
"Holidays were great," he said. "We have a little farm in Canada we go to. ... It was a little colder than Rocky Mountain skiing. A couple of minus-15 days."
As for things with wife Catherine Zeta-Jones, "Everything’s good with the family," he said. We're all good."
Bette Midler said of Penn and the event, "Everybody's a fan. But his intelligence, sense of humor and sense of idealism in the face of so many roadblocks and constraints – the fact he keeps going – is really inspirational to a lot of people. Sometimes you get exhausted and tired, he doesn't."
In between drinks and dinner – shaved apple and celery salad, prime filet mignon and Chilean sea bass – host Cooper kicked off the event with a video, highlighting the relief work done in Haiti, and a musical performance by Haitian Anaelle Jean-Pierre.
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After several speeches – Emma Thompson kept the crowd laughing with her dry humor – Penn took the stage to thank his supporters before the night's live auction began.
A $40,000 trip to Costa Navarino, a $200,000 day with Bill Clinton, the $100,000 keys to Penn's El Camino and other luxuries later (Martin and Chelsea Handler were in a bidding war over an original Bansky painting, which the Coldplay singer ended up taking home for $650,000), and nearly $6 million was raised for the organization, which was founded in 2010 to provide medical care, food and water, and develop housing following the earthquake.
"When I first arrived after the earthquake, we were managing a camp of 60,000 people. It was the biggest camp in Port Au Prince," Penn said. "To know all those people are in homes and have been relocated because of our program ... to walk through that now piece of land that used to be wall to wall tents, that was pretty moving."
The evening ended with a performance by U2, their first in four years, which had everyone on their feet with Chris Hemsworth and his pregnant wife Elsa Pataky, Emma Thompson and Diane Kruger all moving to the music.
How did Penn make it through such an inspiring night? "Vodka tonic," he joked to PEOPLE. As others noticed, too, Charlize Theron was also there, at his side.
Reporting by MATTHEW COLE WEISS