The couple had been dating each other for last one year, reported Us magazine.
"Sometime over the holidays, they broke up. Her life was getting too crazy and it wasn't something that he wanted to be a part of," a source said.
Neither Johnson, 25, nor Hitt, who is a member of band Drowners, has addressed the break-up report.
They were last seen together back in December 2014 while taking a romantic stroll in New York City's SoHo district.
Johnson, 25, rose to worldwide stardom for her starring role as Anastasia Steele in the hit film 'Fifty Shades of Grey'.