—Kelly Osbourne, dressed as Dame Edna Everage, and fiancé Matthew Mosshart, dressed as Blossom from the hit 90's TV show, staying in character the entire evening at MAC Cosmetics and Rick Baker's Monster Mash in L.A.
—Catherine Zeta-Jones taking her kids out with family to see the hit Broadway show Matilda at the Shubert Theatre in NYC.
—Kevin Hart singing along as Jermaine Dupri spun at Playhouse Nightclub in Hollywood.
—Simon Cowell celebrating a friend's birthday until nearly 1 AM at Pearl's in West Hollywood.
—Chord Overstreet checking out the weekly Sunday Jazz Night on a boys' night out with his dad and brother at The Living Room at the W Hollywood.
—Questlove drumming along to Fiona Apple singing their song "Not About Love" during her concert at the Beacon Theater in NYC.
—Tegan and Sara joining Katy Perry onstage at the Hollywood Bowl in L.A.
–Two-time Olympic Gold Medalist Gabby Douglas kicking off National Teen Driver Safety Week at the Mercedes-Benz Driving Academy at Northridge Academy High School in L.A.
—Alex Rodriguez picking out a Modolo bracelet for himself and a DiModolo necklace for girlfriend Torrie Wilson while shopping in NYC.
—Ethan Hawke sipping a Moet & Chandon mini bottle during the Hollywood Film and Awards Gala at the Beverly Hilton Hotel.
—Curtis "50 Cent" Jackson stopping by the Robert Graham Holiday 2013 Preview event at their showroom on his way to the premiere of his newest film Escape Plan in NYC.
—Jillian Michaels chatting with guests at the Sweat USA fitness launch at the Shore Club in Miami Beach.
—Jessica Stam hanging with Kenny G at Day & Night's fifth anniversary brunch party at Highline Ballroom in NYC.
—Susan Lucci attending the Orphaned Starfish Gala at Cipriani Wall Street in NYC.
—Alexa Chung hosting a Teen Vogue Fashion University panel at The Hudson Theatre in NYC.
—Mark Salling hanging out with friends in a corner VIP booth at AV Nightclub in Hollywood.
—Sasha Pieterse hosting Pretty Pink Beauty Night, joined by Secret of the Islands and Pretty Public Beauty to benefit the Dubin Breast Center, at Tiato in Santa Monica, CA.
–Victoria’s Secret model Nina Agdal having a drink with friends at the opening of Paige Hospitality Group’s The Chester in NYC.
—Million Dollar Listing L.A.'s Josh Flagg and Madison Hildebrand discussing real estate over lunch at '21' Club in NYC.
—Debra Messing and Will Chase checking out the newly relocated Natasha, Pierre and The Great Comet of 1812 in the Theater District of NYC.
—ASAP Rocky and Chanel Iman enjoying a a kale salad together while celebrating a friends birthday at Beauty & Essex in NYC.
—P Diddy cozying up with girlfriend Cassie, and a sampling a glass of wine, in the back booth of The Lion in NYC.
–British royal Princess Eugenie of York dining at new Mexican hotspot restaurant, La Cenita, with a girlfriend in NYC.
—Sarah Silverman surprising the crowd including Bobby Flay with a stand-up act at OneKid OneWorld's A Night of Comedy & Other Awesome Stuff in NYC.
–Korn singer Jonathan Davis rocking out with his little son on stage at his show at the Wiltern in L.A.
–Celebrity trainer Adam Ernster teaching a Booty Blast class presented by Lifescript.com at the Pamper Me Fabulous event at the Hyatt Regency in Huntington Beach, CA.
—Mark Ballas stepping out with friends to catch a performance by DJ Eskae and Lil Debbie in Hollywood.
Sign up now for the Us Weekly newsletter to get breaking celebrity news, hot pics and more delivered straight to your inbox!