Unfortunately, the Public Search API, which was used to find posts from Facebook by hashtag, has been discontinued by Facebook on April 30th 2015. This means that searching for public posts from user profiles containing your keywords/hashtags is not possible anymore!
However, you are still able to include Facebook Pages and Albums as sources on your wall. All public posts published on those are reliably queried and displayed on your Walls.io social hub. Optionally, you can limit the posts to those containing your hashtag by using filters.
Find more details on our blog: https://blog.walls.io/product/facebook-hashtag-search/