Sounds like you are talking about a write-on effect, like Stroke. This effect uses masks for each stroke and animates your drawing underneath the masks to make it look like it’s being drawn on by hand. I’m pretty sure there’s a tutorial on this effect, and also one on using the scribble feature if you want your sketching to look rougher. Both might be by Aharon.
You can make your complete sketch that you want drawn on in Photoshop, and then bring it into AE and mask the strokes and use the stroke effect if you want the solution to be “outside of using the pen tool or paint.”