Don't have any answers but didn't want your post to go unanswered. I think this is a lot more common than you'd think. My ds has stopped now, but this was going on in our house for a couple of years. There have been plenty of threads about other people's dcs doing it over that time.
Help just dont know what to do anymore my 15yr old son is stealing money from me all the time. originally it was to buy food for comfort eating (Like his mother) lol. So I started about two months ago to buy him his own supply of biscuits/crisps for the week. This worked till the past couple of weeks. Wont talk to me about it. Grounding doesnt work.