In an account published by Variety, Cori Thomas said she was a minor when Hoffman exposed himself to her.
Thomas said she spent a Sunday afternoon with Hoffman and his daughter in 1980 when she was a 16-year-old student at the elite United Nations International School in New York, Variety reported.
She has alleged that she was left alone in Hoffman's hotel room after dinner as she waited for her mother to collect her. Thomas said the actor disappeared into the bathroom before coming back and "standing there naked."
Thomas said she was "saved" by her mother arriving downstairs. "I was humiliated. I was so mortified, I never said anything."
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Melissa Kester said she was a recent college graduate when Hoffman allegedly sexually assaulted her while recording audio for the film "Ishtar".
Kester said she "sat in the bathroom crying. I thought, 'Oh my God.' I felt like I'd been raped. There was no warning."
A third woman, who asked to remain anonymous, said that Hoffman assaulted her in the back of a station wagon and manipulated her into a subsequent sexual encounter that left her traumatised, the trade magazine reported.
The new claims by the three women take the number of women who have accused the 80-year-old Oscar winner of sexual harassment to six.
Hoffman's lawyer has denied the claims, calling them "defamatory falsehoods".
The actor had offered an apology to the first woman, who interned on the set of his 1985 TV film "Death of a Salesman."
In a statement, he said the behaviour was "not reflective of who I am."
But he has not commented on the other accusations.
The expose on Hollywood producer Harvey Weinstein's three decades of sexual abuse has opened a floodgate in Hollywood, media and politics ending the career of many powerful men.