After Rapp's allegation, London's Old Vic theater, where Spacey was artistic director for 11 years until 2015, launched an investigation into its former leader.
Spacey is among a handful of entertainment industry stars who have racked up alleged sexual harassment and assault claims in the a year ago, including comedian Louis C.K., actor James Franco, chef Mario Batali, and more.
The gossip site reports that one man told police in April Spacey assaulted him in Westminster in 1996, while two other men approached police in February to report two separate attacks, one in Gloucester in 2013, and another in Lambeth in 2008.
Spacey is now under investigation in both the United Kingdom and the USA for a total of six sexual assault claims.
This brings the number of claims against Spacey being investigated by London police to six - five complaints of sexual assault and one of assault.
In a sneak peek for Andrew Denton's Interview program, Pearce claimed he had a "difficult time" with Spacey on set.
Guy Pearce was a guest on the Australian talk show Interview, which saw the actor discuss his professional career. "Amazing actor; incredible actor". Slightly hard time with Kevin.
Actor Anthony Rapp says Kevin Spacey climbed on top of him and tried to seduce him when he was 14. In November, the theatre's board of trustees announced that 20 men had come forward with claims against Spacey.
Pearce, whose first major Hollywood film was L.A. Confidential, added: "Thankfully I was 29, and not 14".
The Academy Award-winner, with his social media account, stated he had a "lot of respect and admiration for Anthony Rapp as an actor", but he was "horrified" to hear the allegations.
He wrote: "But if I did behave then as he describes, I owe him the sincerest apology for what would have been deeply inappropriate drunken behaviour".