I haven't fished for the big Yellow Fin Tuna with the poppers yet bit I have fished for albies, smaller grade Yellow Fin Tuna, Yellowtail and dorado with the poppers.
For dorado, smaller Yellow Fin Tuna and Yellowtail I recommend the Yozuri hydrotiger poppers. I use the sardine, blue mackerel and green mackerel. You can fish this on the same rod you throw surface iron with. For these smaller fish I use a spinning reel as it is easier. I use a Fin nor 7' 20lb spinning rod mated to a Shimano Twinpower 8000 series spinning reel (this is the Japanese version of the Sustain only better). I usually fish these on 20-30lb string.
If you want to go after the bigger Yellow Fin Tuna with Poppers there are two lures that I would recommend:
Yozuri surface cruiser
and the Yozuri Surface Bull GT popper:
I am planning on using these a lot on my 10 day later this year. I'm using a Ulua 93H matched up with an Accurate 665HXM narrow with 50lb test on them.
There are a couple of ways to fish poppers:
You can either "walk the dog" with them which is a slower steady retrieve which gives the lure a gurgling type action.
You can pop them. In this case you reel the slack up and give the rod a big sweeping motion to get the lure to impart a big "pop" on the water. Reel in the slack and repeat. Try this at a slow speed and then try doing it at a really fast speed to see which the fish want.
The third technique I use is to use the popper like you are skip jigging the iron. I cast it out and let it hit the water. As soon as it hits I start cranking like a madman. The lure will skip and skitter across the surface. This has been more suceesful for me. You will get more boils on the lure this way but less hookups as the fish have more trouble actually catching the lure. IMHO it is worth getting less hookups and seeing tuna come flying out of the water after your lure.
The guys in the Gulf of Mexico do a lot of popper fishing for Yellow Fin Tuna and you should be able to get more info from them.
Hope this helps.