At a lower level (texture) you might be interested in Handy and p5.scribble:
- handy gallery — giCentre
- handy — giCentre
- Using the Handy library — giCentre
- GitHub - generative-light/p5.scribble.js: Draw 2D primitives in a sketchy look in p5.js
You could look into using a PShader – perhaps by browsing shadertoy.com for keywords like scribble, scrawl, hand-drawn, drawing, pencil, pen, charcoal etc.
In general, you might also be interested in looking into some recent impressive CGI rendering techniques called “style transfer”, which specifically maps a hand-drawn style onto a photograph or model.
Edit: for more on style transfer resources for Processing, see: