Earlier, a picture of the 23-year-old "Faking It" star and his girlfriend Bella Thorne had surfaced on his personal account with a derogatory text on top of the photo, reported E! Online.
Soon after the message was made live, some fans quickly criticised the actor for his inappropriate language.
Sulkin, however, took to Twitter and said he was not behind the post by any means.
"Unfortunately my social media accounts were hacked yesterday and my phone was stolen. Things were posted to my account that I find appalling and unacceptable. I believe that being part of a religious minority myself, racism is an ignorance that I do not and will not tolerate in my life.
Thorne had also tweeted that her boyfriend had "lost his phone" and that whoever was tweeting was not him.