In a very long and detailed Facebook post shared Monday, Cohen, 27, alleged that the 30-year-old actor raped her three years ago at his apartment.
Westwick has since made a statement via his Instagram account, denying the allegations.
His statement read: 'I do not know this woman. I have never forced myself in any manner, on any woman. I certainly have never committed rape.'
Cohen, who has played minor roles in several movies and TV series, said the alleged rape occurred while she was visiting Westwick with her then-boyfriend, who is not named but referred to as a producer who was friends with the actor.
Cohen claims she laid down in Ed's guest room because she was 'tired', and eventually fell asleep.
The actresses lengthy post then explains: 'I was awoken abruptly by Ed on top of me, his fingers entering my body. I told him to stop, but he was strong. I fought him off as hard as I could but he grabbed my face in his hands, shaking me, telling me he wanted to f*** me. I was paralyzed, terrified. I couldn't speak, I could no longer move. He held me down and raped me.'
'It was a nightmare,' she continued. 'And the days following weren't any better.'
The actress said the producer blamed her, saying she was an 'active participant' and couldn't report the incident because Westwick would allegedly have people 'destroy' her and her acting career.
Cohen said she felt inspired to come forward with her story by the numerous sexual assault allegations currently rippling through Hollywood and society in general. Cohen said that even now, she grapples with 'feelings of guilt.'