A Study of the “Human Flesh” Search Engine (2010) [pdf]
u.arizona.edu
u.arizona.edu
The phenomenon is interesting as one example (among many others) of the democratization and 'cutting out the middle man' that the web offers: citizens taking legal and ethical matters into their own hands. It relates to things like the #metoo movement and Anonymous in the west.
Ultimately these 'courts' tend to devolve into witch-hunts and mob rule without possibility to appeal, but it doesn't mean that they don't play some positive role - in nudging law enforcement to step up their game if nothing else.
This document doesn't explore those aspects however.
One takeaway (certainly not the only) from the paper is that most research is done by a few participants, even as participation size increases.
As for the muscle-powered, on page 4 of the document there's a graphic that shows the ratios, and it's no contest. The vast majority are involved in announcing (the situation) and uploading / re-uploading (the information). Informing and spreading.
It's obvious to me in hindsight, but I wasn't expecting such a wide gulf.