The way to do it easily - and the way I think it was done - is to shoot this as a practical effect. In other words, put the background art on a table and use a charcoal pencil to draw the line in slow motion (the original was probably shot with a high-speed camera). It could also be done with a couple of particle effects and a 3D hand and charcoal pencil - which would be much more time consuming, and nowhere near as convincing as the real thing.
Looks like you are on the right track. Personally, I'm pretty new to AE, and still learning. It looks like you could add some smoke or splats that are the same color as your smoke. It looks like in the movie trailer, there are some composite like splashes or overlays that are dark colored to make it look like the charcoal exploded when it got dragged across the paper.