Advice on getting my arepas to "puff"?
Hmmm...

You can try baking powder. Personally, I am not used to puffy arepas, they are usually dense, and different totally from tortillas; but if you want to try, it would go better with baking powder than with yeast.

Try to precook them in the oven (low - mid) before putting them in the 'budare' / griddle.

Sumito Estevez is a well-known venezuelan chef, I would suggest you to check this one.

http://elgourmet.com/receta/tres-desayunos-arepa-granola-y-omelette