Where I lived before, there used to be a black GSD who the owner could not control, he used to frequently escape his owner and we would hear an almighty racket as he chased after every cat he could see, believe me he did not want to say hello,

he would have happily ripped them to pieces if they had been caught.
Even dogs which live with cats still chase and would hurt another cat, so it would not be a good idea to introduce this young dog to the cats he is so eager to find, not to mention the cats would probably give him a good scratch on the nose for getting too close, which could cause not just him whining and pulling to get to them, but ferocious barking at the next meeting.
If it were just to teach him not to pull on the lead, I would advise as suggested, the stop and start, and walk to heal with treats, but to be honest, the best action is probably to pop a ball in his mouth and get passed as quickly as possible, whilst young this is a natural instinct and not something that can be curbed some breeds are worse than others, once he is an older dog if not allowed to chase cats will not be quite so interested.