Not to mention yorkies are susceptible to collapsed trachea's...and using a leash that attaches to the neck can be very damaging. Using a harness eliminates that danger.
BOTH of the yorkies me and my sister adopted were walked with leashes that attached to the collar..and BOTH of them have collapsed trachea's.
The only thing I can tell you is just keep working with him...if he's 2 and never been on a leash he's not going to understand how it works right away...once you have his 'harness' on him...just pull slightly and as he moves let up on the leash...if he stops tug again..but as soon as you get him moving release the tension again...if you keep working with him...eventually he'll learn to walk "with you".
All dogs need to be trained to walk with leashes...so don't get discouraged...but keep working with him. He'll get the idea...