· Hashtag search was deprecated in FB Graph API v2.0 . Keyword search is also deprecated
· Querying hashtag with FB Graph API v1.0 only works for facebook Apps that are created before April, 30th 2014
· A valid access token has to be used
· The researched term has to be preceded with “%23” in place of “#” , So to retrieve posts of hashtag “https://www.facebook.com/hashtag/crime” use %23crime
Search API is randomized and no 100% guarantee what you expected to see even though you can search facebook.com/hashtag/mystory doesn’t means you can get the results from API calls. You can get crime response because this hashtag is famous, Moreover this feature is deprecated.
So,Facebook Api index only posts with a certain amount of views during a certain period of time.A post could be indexed in the FB api when it reaches a number of views and then disappear when this amount of views decrease on a time period. In other words, only posts with a current high reach are indexed in the api.