You must be wondering why there is no option for Facebook Hashtags in Taggbox Social Wall. So the reason behind is that Facebook has stopped supporting API for Hashtags on April 30, 2015.
A Facebook spokesperson said, “We made this change because we heard from people that they want more control over the information shared with apps. The Post Search API allows apps to access public posts of people who may not have logged into the app, so we’re deprecating this API to give people more control over how their information is used by apps.”