But right now it looks a little strange, sort of separated lines of smoke but not patched together as a whole, dunno if I explain it correctly.
That's what I've done (if someone wants the Particular settings or after effects project, please let me know):
1) Created a matte for just the sweatshirt with Primatte Key.
2) Imported that into the main composition. This will be the "emitter" layer for particular.
3) Duplicated layer and remove Primatte key. So I have exactly the same footage to work on.
4) Apply Particular to a New solid layer. Set the emitter to "emitter" layer on step 2.
5) Work on Particular, but on the Aux. System, this is what will emit continually and create the illusion of smoke emitting from the sweatshirt. The Main particle is hidden, either by lowering the opacity to 0 or creating a null layer, and using it as custom particle. I've tweaked the gravity, wind, and so on, so it kinds of move with along with the footage. I've also activated motion blur.
6) Apply Glow and little Gaussian blur to Particular layer.
7) Created a Displacement map, so it gives some weird smoky distortion to the footage.
So, what do you think? Any ADVICES will be really appreciated, A LOT, because I'm pretty sure it can be better, but my knowledge of After effects has been reached ;)