Very cool tool Tagboard lets you do just that.
Tagboard, which recently celebrated its one-year anniversary with a design overhaul, creates hashtag hubs so you can see a tiled display of mentions of any hashtag across Twitter, Vine, Instagram, Facebook, App.Net and Google+.
From the Tagboard homepage, you can view sample tagboards of currently trending hashtags, or create your own.
Then on the individual tagboard screen, you can toggle between each social network to see hashtag mentions specifically there, or else view all at once.
Tagboard enables social sign-in for Twitter, Facebook, and Instagram, with which you can comment, like/favorite, share, create tagboards, and more.
Further, there is a Tagboard browser extension for Safari and Chrome that lets you search for a hashtag from your browser bar.
What would you use Tagboard for?