I would be going back to the dead basics.
-Leave the door closed.
-Bring him out every hour or two to go to the bathroom.
-As this progresses and you trust him more, extend the time between going out.
-Get a black light to check for mistakes
-Get an enzyme cleaner ie OUT or Nature's Miracle for old and new messes
-If he plays and has a RLH take him out right away on a leash after he is done
-30 minutes after he eats take him out to do poos
-Praise the heck out of him when he goes out.
-Ply him, bribe him with treats if you have too!!~can work in your favor or nip you in the butt!
-If after 5-10 minutes nothing. Put him in a crate for a bit and try again.
After he gets the idea that outside is to do business 1st and play second you can try keeping the door open again, but still leashing him and sending him out. Soon he should get it and be out on his own!
This is method we use and used in the past. Sully doesn't get treats for going out side as he is already house trained. But, he is leased when he goes out till after he does his bid-ness!