Also, one other cool thing I discovered is now thanks to the update, if your looking for a particular Mii, you can make one similar to the one your looking for, name it something like "S. Colbert" if you were trying to find steven colbert mii's. Then upload the one you created, and when you view it, it gives you the option of calling his/her friends.
If the whole 2 letter search doesn't work for you