This article I found on Business2Community is a really great guide to using hashtags on Google+ (and also how not to use hashtags on Google+). The infographic gives a really clear outline of the best ways to use hashtags to reach broader audiences that are more likely to share your messages.
“Hashtags have been around for a while now and most of us are probably familiar with them as they relate to Twitter. Hashtags exist to help people find and participate in conversations on topics that interest them.
For marketers, it is important to pause and think about which hashtags to include or not include in our posts because this will have a big influence on who discovers (or fails to discover) what we are posting about.”
Read More: On Business2Community