To the right of each abstract, SSRN displays a blue box with "Paper statistics." For some papers, that includes "Citations."
For example, next to Cash for Kidneys? Utilizing Incentives to End America's Organ Shortage, 13 Geo. Mason L. Rev. 69 (2004), by Prof. Steve Calandrillo, there's a box indicating (as of July 1, 2016) that the paper has been cited twice.
By clicking on the Citations link, one can see the two papers that cite Cash for Kidneys.
Does that mean the paper has only been cited twice?
No! Why not?
KeyCite on Westlaw shows 47 citing references for Cash for Kidneys, 1 treatise and 46 law review articles. A full-text search in Westlaw also shows it cited in Virginia's annotated statutes.
In June 2016, SSRN released a full-text search option. Now researchers can search the words in the posted papers, not just title, abstract, and keywords.
Searching for calandrillo cash for kidneys yielded 17 papers, including the two found by the automated citation searcher.
For example, we see that Cash for Kidneys was listed in Louis J. Sirico, Jr., Donating and Procuring Organs: An Annotated Bibliography, 104 Law Libr. J. 285, 297 (2012), which could be very useful for a researcher who wants to pursue the topic of organ donation further. We also find that Prof. Calandrillo's paper was cited in Code, Nudge, or Notice?, 99 Iowa L. Rev. 773, 785 n. 71 (2014), by Prof. Ryan Calo, a paper that could lead a researcher from the topic of organ sales to broader issues of law and policy.
Using the full-text search is broader than the built-in citation links, but it still only covers papers that are posted on SSRN.