Ask HN: Search engine to find references to URLs

It occurred to me recently that it would be useful to be able to search for web pages that reference a particular page of interest, as they are likely discussing similar topics and may have further useful insights into the original content. In some ways linking produces a directed graph of related content, and I would like to be able to traverse this graph.

It occurs to me (from a very high level) that this sort of data is at the core of a page-rank type search engine so I assumed such a thing probably already exists, however I don't seem to be able to find anything like it. Most similar sites appear to just find links to domains. Is anybody out there aware of such a search engine?