We've seen a lot of this # on Twitter.. And honestly, I could never imagine having it on Facebook too!
Support for the all-but-ubiquitous topic organization system was rumored in March and will roll out to a small percentage of users Wednesday. Facebook will roll out hashtags to more users in the coming weeks.
The social network wants to make it easier for users to find content already on Facebook, and functional hashtags are the first step. According to Facebook , many users already post hashtags anyway, so why not make them work. Hashtags will be both clickable and searchable, so, for example, topics like #NSALeaks or #NBAFinals will now exist.
Hashtags from other services, such as Instagram, are clickable as well. Users will also be able to compose posts directly from a hashtag feed and search results. That could make adding real-time content to specific streams easier than before. [Source]