Hashtags are supported on all social networks (Twitter, Facebook, LinkedIn, Google+, Pinterest and Instagram).
They can be added to your post in the same way that you would add them to the social networks natively, by typing # followed by the tag you'd like to share, e.g. #socialmedia.
Keen to learn more about using hashtags effectively in your social media marketing? Why not check out this Buffer blog post? How to Use Hashtags: How Many, Best Ones, and Where to Use Them