When someone performs a search on a search engine and is presented a result page, he is a click away of becoming a visitor of one of the listed links. If you own site appears in the list, you could consider this person as a "potential visitor".
However, "potential visitor" sounds a bit unclear. For example, this term could be used to designate someone who might be interested in the site at a later time, but this is not what we mean here. Is there a more specific term to name this person?