How Female Stars Honored International Women's Day

— -- A bunch of female stars disappeared on social media Sunday.

Amy Poehler, Cameron Diaz and Lupita Nyong'o were among those who replaced their social media profile photos with a faceless avatar in honor of International Women's Day on Sunday.

The stunt was part of the Clinton Foundation's #NotThere campaign to call attention to gender inequality around the globe. Chelsea and Hillary Clinton led the way by swapping out their Twitter profile pictures.

Celebrities quickly followed suit.

"We're Not There ... Yet," Diaz wrote on her Instagram account. "Inequality exists at work / at home / at the doctor's office / at school - and yet these issues do not get the attention they deserve. It's almost like we're NOT THERE at all."

On her Instagram account, Nyong'o wrote, "For International Women’s Day, I am taking a stand for gender equality and I'm joining others to be #NotThere."

In addition to the social media campaign, the Clinton Foundation cut out women in dozens of existing ads, magazine covers and posters. Thus, Rosie the Riveter vanished from her iconic poster on a bus shelter in New York City and Serena Williams disappeared from a giant Beats billboard in Times Square.

Poehler, Diaz and other female celebrities explained the effort in a video on the campaign's website.

Other stars marked International Women's Day with their own messages.

"Girls" star Allison Williams gave a fist bump to her co-stars on Instagram.

"So thankful to have so many strong women in my life. We're not there yet, but we're getting there. Going to be spending it with my GIRLS family at PaleyFest," she wrote.