Molly Sims and Kristen Bell belted out tunes for charity at the UNICEF Playlist With The A-list event, held at El Rey Theater in Los Angeles. "TONIGHT is the night! Come see ME bust out some karaoke w/friends for @UNICEFUSA!" mom-to-be Sims Tweeted last night. Heidi Klum and Tom Bergeron also lent their voices to the cause, which raised money for the charity's Schools for Africa program. Click through the gallery to see more stars at last night's hottest parties.