“Saw” star Leigh Whannell and Caitriona Balfe have signed on to round out the cast of Intrepid Pictures’ thriller “Crush,” which starts principal photography this week in Los Angeles.Malik Bader is directing from a script by Sonny Mallhi (“The Roommate”). Lucas Till (“X-Men: First Class”) stars alongside Sarah Bolger, Crystal Reed, Reid Ewing and Camille Guaty. Till plays a star high school athlete who becomes the focus of a secret admirer’s obsession. He soon discovers that the innocent crush has turned dangerous and deadly. Whannell will play the owner of a local yogurt shop, while Balfe will play the owner of a comic book store where Reed works. Intrepid is fully financing the pic, which is being produced by its principals Trevor Macy and Marc D. Evans. Mallhi will exec produce with Intrepid’s Anil Kurian. Glen Basner’s FilmNation will handle international sales, which will commence during next week’s AFM. U.S. distribution rights are still available. Whannell, who co-created Lionsgate’s boffo “Saw” franchise, most recently wrote and co-starred in James Wan’s “Insidious,” which has grossed $92 million worldwide on a miniscule production budget. Balfe recently appeared in J.J. Abrams’ “Super 8.” Thesp will next be seen in Bryan Singer’s sci-fi web series “H+” and “City of Jerks” alongside Kelly Blatz and Joelle Carter. Whannell is repped by Paradigm and Stacey Testro International, while WME and Patty Woo Management rep Balfe.