Aspiring stars can upload their performances on a new website, which has been launched to find new young talent. According to the BBC, nearly 100 people have submitted videos for the three junior lead roles.
Submarine, based on a novel by Swansea-based author Joe Dunthorne, is being directed by Richard Ayoade, whose credits include The IT Crowd and The Mighty Boosh.
The film follows the story of Swansea teenager Oliver Tate, who attempts to woo a girl called Jordana while also preventing his mother from leaving his father for a dance teacher.
Producer Warp Films is still recruiting for the roles of Oliver, Jordana and Oliver's friend Chips.
Sheen and Hot Fuzz's Paddy Considine have been cast in the lead roles.
Warp Films's Grant Keir said: "This gives young actors the chance to join an A-list cast that Warp Films have already secured, including Michael Sheen of Frost/Nixon and Paddy Considine of Hot Fuzz."