Starting today, hashtags will be clickable on Facebook. Similar to other services like Instagram, Twitter, Tumblr, or Pinterest, hashtags on Facebook allow you to add context to a post or indicate that it is part of a larger discussion. When you click on a hashtag in Facebook, you’ll see a feed of what other people and Pages are saying about that event or topic.
Now you can:
• Search for a specific hashtag from your search bar. For example, #NBAFinals.
• Click on hashtags that originate on other services, such as Instagram.
• Compose posts directly from the hashtag feed and search results.
As always, you control the audience for your posts, including those with hashtags.
http://newsroom.fb.com/News/633/Public-Conversations-on-Facebook