Can Twitter really help to get users to a community site, and why?

It would more likely be by word of mouth.

Your followers will probably have something in common with you, and if the site if of sufficient interest then they will pass the info on to their follows, and if you get lucky it starts to get passed around, and many people can be informed.

If they are informed about a site by someone that they know (using that term loosely) then they are more likely to at least look at it.

I don't recommend you think of Twitter primarily as a tool to drive traffic. Twitter has its own dynamic, and the Twitter community is not very receptive to tweets that represent fairly blatant attempts to get them to visit a particular site.

What are you offering on your community site? Offer the same thing via Twitter, albeit in a much more concise form. Then, sure: include a link for those who found value in what you tweeted and want to know more. But the tweet must stand on its own.

Of course, if you are a rock star or some sort of net.celebrity, you can get away with tweets like "Just got a new car. I like it, but I miss my old one." For the rest of us, it's content that counts.

Twitter is the No.1 marketing/networking tool out there, but it has to be used with some skill.

Use it to:

1. Engage with them don't just spam them.
2. Find your audience.
3. Use it to find influential people in your market.
4. Follow them.

A friend of mine has a community based start-up He uses twitter along with FB to gain traction.

Using twitter, FB and email marketing, he basically manages to quickly "communicate" the latest happenings to the actual users and potential users.

In fact users themselves do this, he just facilitates the communication.

Idea is to fuel the viral loop as long as possible. If your website manages to fuel it for considerable lengths of time, you have a bright chance to be the next FB.

Twitter will only be good for your business if that's where your target audience hangs out.

If your audience is mostly on Facebook or LinkedIn, then that's where you should be focusing your attention. It's not about Twitter being right or wrong, it's about it being the right place to find your audience.

This is where marketing personas can help a lot.

Come up with the notion of your ideal customer. What are his or her pain points that you can solve? Where does s/he work? Where does s/he live? What does s/he look like? What's his or her name? Really flesh this "person" out so that you almost feel like they're a friend or acquaintance.

Once you come up with a marketing persona and can put yourself in the mind of your target customers, it'll be easier to figure out if Twitter is the right place to reach them.

If it is, then I'd highly recommend HubSpot's "Twitter for Business" kit, featuring videos, eBooks and articles about how to use Twitter effectively for your business. Lots of great stuff.

http://www.hubspot.com/twitter-for-business-marketing-kit/

Disclaimer: I work at HubSpot.