There's actually a great way to use the footprint functionality by triangulating the pokemon's relative position. Try the following and it will work for you every time (unless there's an in-game glitch, of course, *ahem*, but the mathematics are sound...)
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Let's say you have a Pokemon with 2 footprints showing on your radar. (if you do not, walk until you DO have one with 2 footprints).
Now, choose a direction and walk that way in as straight a line as possible (doesn't have to be perfect). If the footsteps increase to 3 immediately stop, note the general location of where you have stopped, then turn around 180 degrees. Walk back the way you just came. It will eventually decrease to 2 again.
Keep walking. Unless you just got lucky and are now heading straight to your Pokemon, the steps will eventually increase to 3 again. Stop. Turn around. Look back and eye the general location where you stopped in the other direction and try to gauge the midpoint between that spot and where you are now. Walk to the midpoint.
In the middle, between the two locations where the pokemon's distance became 3 prints away, you choose either left or right and walk. You will either head directly into the Pokemon or directly away from it, which is easily corrected when you see the steps increase.
Works every time, as long as you don't have buildings in your way.