She said police on Nantucket island in MA are now investigating a report the young man has filed.
A former news anchor has accused actor Kevin Spacey of sexually assaulting her 18-year-old son, leaving him traumatised.
She said Spacey tried to get her son to go with him to an after-hours party.
Kevin Spacey has at least one person defending him from the onslaught of sexual misconduct allegations, of varying degrees of severity.
"My son is anxious, but he is also confident the time to act is now", she said.
Ms Unruh said embarrassment and fear meant her son did not inform authorities at the time, but that he had filed a police report following the tide of allegations against Harvey Weinstein last month.
The press conference came nearly a month after Unruh first tweeted that Spacey, 58, had assaulted a loved one of hers. That was an appalling attempt to deflect attention from what you really are: a sexual predator.
"There was no consent", she said.
She added, "Time the dominoes fell". Last week, a representative said the actor - an Academy Award victor and star of the Netflix show House of Cards - was "taking the time necessary to seek evaluation and treatment" and that "no other information will be available at this time".
"Shame on you for what you did to my son", Unruh said at Wednesday's news conference.
Kevin Spacey attends the Build Series to discuss his new play "Clarence Darrow" on May 24, 2017 in NY.
"Reports of sexual assaults are confidential under [state law]", the spokesman says. A publicist said last week that Spacey is "taking the time necessary to seek evaluation and treatment".
The writer also compared Spacey to the Dalai Lama, who likely "has done something he's ashamed of".
Spacey apologized in an October 29 tweet - his last - but also said he had no memory of the alleged encounter.
Mr Spacey and surrogates have not specifically addressed any other allegations since Mr Spacey responded to Mr Rapp's accusation.
The family lawyer also told reporters Wednesday that his client had spoken to Nantucket police, who were investigating.
Since the allegations surfaced, Netflix has severed its ties with the actor, and the producers of his show, "House of Cards", have suspended him "effective immediately".
Spacey has been accused of groping Rapp, a star of "Star Trek: Discovery", and Richard Dreyfuss' son, Harry Dreyfuss, among others.