How to Follow a Hashtag Across Twitter, Google+, Instagram and Facebook
Posted on November 18th, 2013
One solution I found is Tagboard, "the social media hub for hashtags."
The free service doesn't allow for complex search combinations (yet), but its clean and results-oriented user interface makes the wait for future improvements worthwhile.
You can simply log in with your Twitter or Facebook account. Tagboard allows for easy sharing of hashtag boards directly into Evernote, for example into your Postach.io blog notebook.