I think the suggestion is that you first look for questions with the hashtag and then if you don't find any look for questions the way you currently are. That

I think the suggestion is that you first look for questions with the hashtag and then if you don't find any look for questions the way you currently are. That way a small user base can make use of the feature but for everyone else it stays the same. You should also take a look at youasked.it. They're very similar. I think giving the user a chance to filter questions by topic is a very key feature that is missing right now from your implementation.