If you have a Disney VISA card, there is a special "meet and greet" at Futureworld. THe characters rotate, but we've probably done this a dozen times and 10 out of the 12 it was Pluto and either Mickey or Donald, lol. The nice thing about the VISA meet/greet is that you go into a room with the characters all by yourself, so you can really get some great interaction going with them, and pretty much spend as much time as you want. My girls usually get them dancing, lol.
Pluto is all over the place, like others have said, that those are great ways to meet him too.....I just really loved having the extra "private" time at the VISA. If you don't yet have a Disney VISA, seriously consider it....no annual fee, typically they have gift card offers for signing up, you earn Disney dollars for every dollar you charge (I charged everything, including bills, on that card so we'd have a bundle to spend our first trip, lol.....now I'm not quite as intense about using it, but we still manage to earn quite a bit each month). PLUS...you get benefits like the meet and greet, which includes a print out of a photopass photo......and typically Disney offers discounts to VISA holders either before the general public, or sometimes they are exclusive and the general public never get the same offers. We got free dining last Nov/Dec because of that VISA card! By the time it was offered to the general public there were no more rooms with free dining at the hotels of our choice for our Thanksgiving week before and week of visit.