Heather Kerr, who appeared on 1980s US sitcom The Facts of Life, claims Weinstein attacked her during a private meeting with the producer when she was an aspiring actress in her 20s.
"He asked me if I was good. I started to tell him about my training and my acting experience and he said, 'No. I need to know if you're good,'" Kerr, who is now 56 and lives in Washington state, told a news conference.
"He said that if he was going to introduce me around town to directors and producers, he needed to know if I was any good. He kept repeating that word."
Kerr described 65-year-old Weinstein's "sly, sleazy smile" as she offered to provide a reel of her acting work, recalling how she started to get a sick feeling in her stomach.
"The next thing I knew, he unzipped his fly and pulled out his penis," she said, adding that Weinstein forced her hand onto his genitals.
"I was frozen with fear, trying to remain calm, trying not to freak out, because, after all, there was nobody else in the office," she said during an emotional statement, consoled by her attorney Gloria Allred as she broke down.
Kerr described how she pulled her hand away "as casually as possible," but said Weinstein told her that "this is how things work in Hollywood," and that all actresses who'd made it did it this way.
The veteran producer, who resigned from the board of The Weinstein Company this week, having already been sacked as its co-chairman, has so far denied all allegations of forcing himself on his accusers.
An Italian model and actress who says Weinstein raped her after dragging her into the bathroom of her hotel suite in Beverly Hills in 2013 also spoke out about the attack Friday, through her lawyer Dave Ring.
The incident occurred at the Mr. C Beverly Hills hotel after she attended the 8th annual Los Angeles, Italia Film, Fashion and Art Fest in February 2013, according to the attorney.
"He bullied his way into her room. She has told me that obviously her greatest regret is opening that door. She had no idea what was coming," Ring told a news conference in downtown LA.
The actress, who is exercising her right to anonymity, first spoke of the attack to the LA Times on Thursday, saying Weinstein had turned up at her hotel "without warning".
"Once inside, he asked me questions about myself, but soon became very aggressive and demanding and kept asking to see me naked," the Times quoted her as saying.
"He grabbed me by the hair and forced me to do something I did not want to do. He then dragged me to the bathroom and forcibly raped me."
Ring told reporters the incident "had a humongous, huge impact" on the mother-of-three, who is now 38.
"In a sense, she's relieved to have come forward now, to be able to share what happened with the LAPD, but she's also extremely scared, and rightfully so. She's a mom. She has young children."
He didn't elaborate on the details given in the newspaper interview, however, saying he did not want to jeopardise the investigation.
Los Angeles police have confirmed they are looking into the case - the sixth rape allegation against Weinstein - adding to criminal investigations already underway in New York and London.
The latest case deepens the producer's potential legal woes as it falls within the 10-year statute of limitations for the crime, while previous accusations have dated back to a decade or more ago.
Weinstein has become a Hollywood pariah since allegations about his sexual misconduct first emerged last week and he was kicked out of Hollywood's motion picture academy.
The Television Academy's governors voted late Thursday to begin "disciplinary proceedings" that could see Weinstein ousted from that organisation as well, leaving him with no voting rights for either the Oscars or the Emmys, while the Producer's Guild is considering following suit.
A representative for Weinstein told the celebrity news website TMZ that after completing a one-week program at rebab in Arizona, that the disgraced producer would "stay in Arizona for another month or so because he doesn't want excessive distractions and wants to continue working with his doctors."
Weinstein's lead psychologist told the website with his permission that he had been "dealing with his anger, his attitude toward others, boundary work and the beginnings of work on empathy."
Director Weinstein was "invested in the program," the psychologist told TMZ.