She shared a note from a friend, which read, "If all the women who have been sexually harassed or assaulted wrote, 'Me too' as a status, we might give people a sense of the magnitude of the problem."
As of Tuesday morning, more than 1 million tweets have included the hashtag, along with more than 12 million posts, comments and reactions happening on Facebook.
Late Monday night, the "Superstore" star, 33, posted on Instagram that she was sexually assaulted at age 9.
"I told no one and lived with the shame and guilt thinking all along that I, a 9-year-old child, was somehow responsible for the actions of a grown man," she wrote in a heartbreaking post.
She added, "I had to see this man on a daily basis for years to come. He would smile at me and wave, and I would hurry past him, my blood running cold, my guts carrying the burden of what only he & I knew — that he expected me to shut my mouth and smile back."
Ferrera concluded, "Ladies, let's break the silence so the next generation of girls won't have to live with this bulls***."
On Facebook, Elizabeth Warren and actress Jeri Ryan have also posted, "me too."
It wasn't just women speaking out; some men did as well.
In addition to this campaign, Milano also addressed the Weinstein situation last week on her blog, "Patriot Not Partisan."
"To the women who have suffered any form of abuse of power, I stand beside you. To the women who have come forward against a system that is designed to keep you silent, I stand in awe of you and appreciate you and your fortitude. It is not easy to disclose such experiences, especially in the public eye," she wrote.
Now, in response to the allegations directly against Weinstein, a spokesperson for the movie executive said, "Any allegations of non-consensual sex are unequivocally denied by Mr. Weinstein."
"Mr. Weinstein has further confirmed that there were never any acts of retaliation against any women for refusing his advances. Mr. Weinstein obviously can’t speak to anonymous allegations, but with respect to any women who have made allegations on the record, Mr. Weinstein believes that all of these relationships were consensual," according to the full statement from Weinstein's spokesperson. "Mr. Weinstein has begun counseling, has listened to the community and is pursuing a better path. Mr. Weinstein is hoping that, if he makes enough progress, he will be given a second chance.”
Weinstein was fired from The Weinstein Company, which he co-founded, and has been expelled from The Academy of Motion Picture Arts and Sciences.
"The Academy of Motion Picture Arts and Sciences Board of Governors met today to discuss the allegations against Harvey Weinstein, and has voted well in excess of the required two-thirds majority to immediately expel him from the Academy," according to a statement issued on Saturday from the organization.