Midrub has a new feature, which allows to get popular hashtags based on a word or hashtag. This feature could be enabled first from the Admin -> Posts -> Enable Hashtags Suggestion Once enabled from admin, users will see the option in Users -> Settings -> Posts. By default only Twitter Hashtags is enabled, but if for the user plan is enabled Instagram Insights, will be available even Instagram Hashtags Search.  

I’ve added hashtags support for Tumblr and Medium and i think to add for the next update support even for Imgur. The hashtags support don’t has a special field. You have to use #. For several social networks is not required support because them recognizes the hashtags via #. I think to add mention support in the same easy way but by using @.