Send him to live with his twin for the next 6 months!
No seriously when Michael was doing this same crap as it seems most teenage boys do these days,
I took the door off of his bed room so he had no privacy, I gave him one full day to clean up his crap or I was going in with a trash bag and throwing everything away that was not picked up and evertime I found something on the floor after that I told him I would warn him once and throw it away as well!
HA HA!! He thought I was bluffing!!!!
Needless to say he was dumpster diving for his crap later that night and it worked for a while, but on occassion I still had to throw something away. Follow through! Follow through! Follow through! If you say your going to do it DO IT!