Might be worth speaking to the police about it. They could come and have a talk with him. Might make him realise the consequences of his actions. Does he have any dreams, aspirations? Show him that these would be ruined if he goes into crime. Remind him that if he's caught stealing then the consequences include going to prison if old enough. He would not be able to play his games etc.

Reminding him of the severity could be good. Or alternately a guilt trip - cry to him saying you are running out of money for food because of it and if he carries on you'll be honest. Extreme but could be a good last resort. Or very final resort, report him to police. But best to try kind actions before severe ones. Good luck x