I found a new Twitter service the other day called We Follow - which calls itself a 'user powered Twitter directory'.
I like the look of WeFollow, just because it's so simple and uncluttered, but you can only add yourself to three categories, which is a bit frustrating. A lot of individuals, and a lot of charities, are a lot more multifaceted than that.
I've signed up to We Follow anyway though - because directories are a good place for other people to find you, so can help you attract new followers. And because people find you via a category search, like 'nonprofit', it's likely you'll share a genuine interest with them, so it's a win win.
If you're a charity and followers find you using a directory, the chances are that they are pretty interested in what you do - exactly the sort of people you want to engage with.
At the moment, Twellow is more searchable, because you can add far more categories to your profile, which creates more ways for people to find you. Twellow also allows you to link to more of your social profiles, which makes it easy for people to engage with you on the platform of their choice.
There are plenty of other ways for your supporters to track down your Twitter profile, including promoting and linking it to your Facebook page, your YouTube channel, your website - all of which will help bump the page rank up in searches.
There's also Twitter Search (which has recently added an advanced search, which helps you drill down further into niches and interests).
I would still say it's worth registering with directories though, just so you are covering as many bases as possible and making it really easy for people to find you and engage with you.
Like Twitter search, they'll help people find you based around their interests, rather than by your brand - and that's very powerful.
Come to think of it, Twellow automatically creates a listing/ profile for you when you start using Twitter, which you have the option to claim and amend or add to. Have you claimed yours yet?