How many pads do you have down? Sometimes having too many targets creates confusion. I would limit it to 1, or if you have a 2 story house, 1 upstairs and one downstairs.
Start with limiting his freedom in your home to a smallish area with the pad. Supervise, praise profusely when he gets it right and give him a small food reward. Praise and reward for outdoor potties too. Never stop with the praising.
When he gets it wrong, don't scold him. I would say "uh oh" and bring him to the pad and remind him with keywords and phrases that it is the correct place to potty. You also need to clean up and remove the scent from the accident spots, otherwise he will be tempted to return. Use an enzyme cleaner.
Here are some more tips in my blog:
Potty Training Small Dogs - Dog Life and Style