Does Google use site wide signals to determine the position of new web pages in the search results? Google’s John Mueller commented on this in a Google+ hangout:
For the most part, we try to understand the content and the context of the pages individually to show them properly in [the] search [results]. There are some things where we do look at a website overall though.
For example, if you add a new page to a website and we’ve never seen that page before, we don’t know what the content and context is there, then understanding what kind of a website this is helps us to better understand where we should kind of start with this new page in search.
So that’s something where there’s a bit of both when it comes to ranking. It’s the pages individually, but also the site overall.John Mueller, Google
You can view the video here: