Participating in hashtags is a solid method for getting more impressions and interactions on your individual tweets. The more impressions you have, the more likely people are to see you and follow you, even if they're not entirely sure what you're about. Rather than trying to sell your whole personality or brand to Twitter users, it really seems that being topical is more important for gaining followers, who will follow you for the input on that one topic, then maybe stick around for the other parts of your Twitter presence afterwards.
ETA: I'll also add to the choir by saying that Facebook is a poor way to self-promote. Facebook only shares out posts from your page to a small amount of the people who have liked the page. If one of those few engages with the post, then it will be shared to others who have liked the page and so on. Twitter and tumblr shares out the post to everyone, and is far more effective, which is why my Twitter/tumblr followers number in the hundreds, but Facebook is sitting at 65 likes. I'll still post updates to Facebook because I can count on at least a few clickthroughs per week, but it isn't a great place to grow your following at all.