Hashtags augment quality posts in Google+; they are not a replacement for posts, however.
In the following screenshot, a guy is sharing his blog post. Ostensibly, having written it himself, he could give us a sentence or two that might compel us to read the article. He would also be able to choose just a few good hashtags that are relevant and likely to reach, one would think. However, All he did was adorn a share of the link to the article with 35 hashtags. Twelve hours later, and he has no interaction on it: no comments, re-shares or even plusses:
Here is a recent post I did, via my friend Robert Fransgaard, on how even some of the biggest companies in the world have hashtags backfire on them. #RIMjobs was not well thought out (Blackberry jobs). It would appear from the interaction I got that I formatted the post well enough, and provide my own thoughts on the post along with just a couple relevant tags:
How do you choose relevant but also reaching hashtags for googleplus?
Do it right inside Googleplus: start typing from the # character, see what comes up, and then click that tag to search posts with the hashtag. Or, to search in a non-alphabetical way, use RiteTag and the search feature within Tag Optimizer (the first thing you land on, once signed in to RiteTag). This is what I do, since RiteTag AI gives me a quick idea of how much a tag is being used lately, and thus, the likelihood that it will be searched.