Friends even had a birthday cake that paid homage to his Calvin Klein ad!
Brittany Snow and her boyfriend attended the bash, but Kellan's on-off girlfriend AnnaLynne McCord wasn't there. How come? She's currently in Cambodia on a charity trip, according to her Twitter.
The couple's still on though...for now. They recently took a trip to San Juan, Puerto Rico, together to participate in Roselyn Sanchez's Triathlon for Life.
Kellan got the party started early last weekend with some help from Twilight costar Ashley Greene when they hit Coco de Ville Friday night with a group of friends and drank Moet champagne and Belvedere vodka.
Ash couldn't make Monday's party, since she's in Austin for the South by Southwest festival.