Several. Scout Willis walked around NYC topfree after being banned by Instagram for posting a topless photo of herself. Rihanna was notoriously banned on Instagram for posting her cover of Lui magazine, which featured her completely naked up top. She also tweeted in support of Scout Willis' “Free In NYC” topless protest.
Rumer Willis has been an outspoken voice of the movement, and is a personal friend of Lina Esco. She even participated in a PSA encouraging women to not be ashamed to breastfeed.
Miley Cyrus has sent out countless topless “Free the Nipple” photos of herself. Other celebrities showing their support include Cara Delevingne, Lena Dunham, and countless others. The latest celebrity (and possibly the most controversial) is Willow Smith.