"At the time of writing, more than 40,000 people replied to her tweet, making "#MeToo" a top trending topic.
Milano, 44, received "me, too" responses from "Will and Grace" star Debra Messing and Anna Paquin, the Oscar-winning actress from New Zealand.
Some men who said they were also victims of sexual assault took to the social media to share their stories, including one of the stars of Broadway musical "Hamilton", Javier Munoz.
Each time this has happened, predatory behavior once shrouded in secrecy, and still tolerated in many settings, has become a little more public.
The campaign quickly trended on Twitter and Facebook, with notable names like Lady Gaga, Monica Lewinsky and Rosario Dawson identifying themselves as victims.
Thousands of women have followed in her footsteps.
A similar social media campaign is playing out on Instagram among models who are sharing stories of abuse and harassment in the fashion industry.
"I feel disgusted and sad", Ed Krassenstein wrote.
Many women in the United States and France appeared to be speaking out for the first time about abuses they had suffered, often saying they had to overcome feelings of shame and embarrassment to do so.
She finally spoke up, using the hastag me too. Twitter briefly suspended her account following the revelations. Alyssa Milano was the first to respond to his own tweet with #MeToo.
In a statement on her website, Milano commented on the situation. The New York Police Department has said it is investigating a 2004 allegation of sexual assault by Weinstein. "I was lucky", one reply wrote. "Men who undermine women and their strength, ability and intelligence exist everywhere".