If you must use AE, you can probably get some pretty decent results a number of different ways. Assuming that this hand is reaching right to left or left to right. If you want this hand to be reaching on the z-axis, it would get a little tricky.
Depending on how you want the fog to look, you could use a layer (a precomp with a hand animation in it) to drive the emitting of particles from Particular.
You could also use that same hand precomp and use Fractal Noise or Turbulent Noise on it. That would just be a starting point. You would probably want multiple copies of the hand layer with various fractal noise settings, blending modes, levels of blur and maybe even displacement maps.
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You could use after effects and particle playground to track your hand and emit "fog style" particles from it to make it look like fog... but it will take a lot of work to make it look decent and you'll need high resolution footage of your hand.
Hit play the video tutorial at the bottom... Perhaps you could film your hand against a static background with the motion and angle you want to use in your finished product, and rather than fire, play with the effects to make it look like fog.
Perhaps in front of a green screen so you can key out the background and over-lay it onto your real footage.