[alaskayorkie]

That would be my suggestion. Go back to the beginning. Find a way to restrict his freedom in the house. For me, that was an X-pen large enough to have her crate on one side and a potty pad on the other. He can sleep in the crate, door open or shut.

Take him out every hour on the hour until he goes outside -- you might even try taking a walk if a short trip outside doesn't work. As soon as he goes, reward and praise.

There should be no unsupervised house time. If you're not directly supervising, aka a leash, he goes in the xpen.

I loosely followed the awesome advice on this site:

Errorless Housetraining | Dog Star Daily