In an article in The Daily Mail David Yates, the director of Harry Potter and the Half-Blood Prince, is quoted as saying he has cast the role of young Tom Riddle.  He does not say who it will be but the writer thinks that Titan Tiffin, Ralph Fiennes nephew, has been cast.:

Titan Tiffin is to be cast as Tom Riddle � the boy who becomes arch villain Lord Voldemort, who is played by Ralph.

‘I’ve found a really interesting kid to play Riddle. I can’t tell you who it is yet � it’s early days.’

For the full text with David Yates click Read More!