The Mexico-born actor, director, producer and campaigner for women’s rights, was addressing an audience in a Q&A session hosted by Nicola Mendelsohn, Facebook’s vice-president EMEA.
She also told the audience that she has just joined Facebook, while tomorrow she is joining Instagram using the handle @salmahayek.
Asked to name her favourite advertising work, Hayek said: "The one I’m most proud of is the campaign I did with Avon. When they came to me they just wanted my face for Avon. I had the choice to do something with a more glamorous company, but I didn’t do that.
"I went to them with a proposition and said, ‘Would you consider working with me on domestic violence?’"
She convinced them and raised more than $90m for the cause. "I used advertising to create a social conscience," she said.
Hayek also mentioned her appearance in a campaign for Bacardi, shot by Mario Testino. "They came to me and said, ‘We don’t want you because you’re pretty, we want you for your personality.’"
Her decision to embrace social media comes despite having largely ignored it in the past.
"I didn’t want to do something everyone else does," she said. "I feel like people are not always so present because of social media. But you certainly can’t denty that it’s a very important part of today.
"Through social media I can have a connection with my fans and I’m excited to discover them. For the first time, yesterday I hashtagged myself."
"Today, you lose your social media virginity," Mendelsohn said.
"Who’s popping my cherry?" Hayek asked.