At least five women came forward this week in a report by CNN alleging sexual harassment while Halperin was the political director at ABC News in the late 1990s.
The women, who were all in their 20s at the time, shared stories of Halperin allegedly propositioning them for sex and making unwanted sexual advances, including allegedly pressing himself against them.
More women have since come forward to allege they either knew about the alleged behavior by Halperin or experienced it themselves.
Dianna Goldberg May, a former ABC News researcher, told The Washington Post that she reached out to Halperin for help with a story but claimed Halperin said he would only help her if she sat on his lap.
"I didn’t know what to do,” May told the Post. “He was important. He wasn’t my superior, but he was certainly in a superior position to mine. I didn’t say anything. I didn’t know how to at the time. I knew it was wrong."
ABC News said in a statement, “Mark left ABC News over a decade ago, and no complaints were filed during his tenure."
Halperin tweeted a statement today saying, "I am profoundly sorry for the pain and anguish I have caused by my past actions. I apologize sincerely to the women I mistreated."
He added, “Towards the end of my time at ABC News, I recognized I had a problem. No one had sued me, no one had filed a human resources complaint against me, no colleague had confronted me. But I didn’t need a call from HR to know that I was a selfish, immature person, who was behaving in a manner that had to stop.”
The women accusing Halperin of sexual harassment said his high position at ABC News stopped them from coming forward.
CNN senior international correspondent Clarissa Ward spoke out on Twitter about the allegations against Halperin, describing his alleged behavior as an "open secret."
Ward, who did not make specific claims against Halperin, worked as an international reporter at ABC News from 2007 to 2010.
Ward also said in a series of tweets that blame should not be placed on the women accusing Halperin or the people they confided in.
"Let's be very clear -- the one responsible for any sexual misconduct that may have taken place is the man who instigated it," Ward wrote.