News Emma Watson, Britney Spears and More Stars Celebrate International Women's Day -- See the Pics! By Jennifer Drysdale 2:16 PM PST, March 8, 2017 The women of Hollywood are joining together to celebrate International Women's Day! From Emma Watson and Britney Spears, to Madonna and Serena Williams, women everywhere are spreading girl power on social media. RELATED: Katy Perry Celebrates International Women's Day With Powerful Message: Now Is the Time We 'Lift Each Other Up' Watson, dressed in a red outfit in support of women, took to Twitter on Wednesday to reveal that she would be handing out feminist books. "Today I'm a red-striking ninja book-fairy out to spread some wise women's words @the_bookfairies #IWDOurSharedShelf #IWD #adaywithoutawoman," the Beauty and the Beast star wrote. RELATED: Emma Watson 'Quietly Stunned' by Photo Shoot Feminism Controversy Spears, meanwhile, paid tribute to the "fierce" women who inspire her, as Williams and Madonna shared their own posts in support of International Women's Day. See more posts below: WATCH: Meghan Markle Shares Inspiring Message on International Women's Day: 'To Always Knowing Your Worth'Meghan Markle Shares Inspiring International Women's Day Message: 'To Always Knowing Your Worth'