Facebook: Facebook only recently added hashtag support in June 2013, and the practice has not picked up much steam. Nevertheless, clicking on Facebook hashtags will take you to a list of posts containing the same hashtag. The results are not limited to people you know.
Google+: When you click on a hashtag in Google+, the search results will include the original hashtag as well as posts with similar tags and keywords. Google search results display on the left side of the page, while hashtag results from within Google+ appear on the right. Google also gives you the option to search within Facebook or Twitter.