When Amanda Rose began was organizing a London Tweet-up with some of her friends in September 2008, she came across some interesting results. By connecting with the right people on the popular social network, she was quickly able to grow an event in two weeks from a gathering of friends to a sold-out 250-person (er, Twitter user) event, all to benefit a local charity.

After the hugely successful first event, attendees began asking when the next one would be. For Rose, the only hurdle was finding a worthy cause to unite individuals across the world to come together to raise funds and awareness for a great cause. She settled on charity: water for their global scale and her own concern for the continued conservation and protection of clean drinking water. When the initial Twestival happened on February 12, 2009, there were 24 different cities signed up around the world to participate. Since that time, volunteers have risen close to $1.2  million for 137 nonprofits and it has become the largest global grassroots social media fundraising initiative to date.

Fast forward to 2011. The Twestival is being localized with individual cities focused on a particular nonprofit in their region. The tagline the organization is “Think global, act local.” Some of their impressive list of sponsors in New York include Hashable, Watchitoo, SnapGoods, Cheek’d, PopChips and more.

““People may say that twitter is useless, but here on the local level it’s affecting real change for real people,” said Ben Meck, Twestival New York City co-organizer. “Twitter is inspiring thousands of people around the world to be more philanthropic, more socially conscious, and more engaged with each other.  Twestival is a great example of that.”

I recently had the chance to catch up with Rose and Meck on the 2011 events, happening March 24. Here are their thoughts:

This will be the third year for Twestival, so what surprises you most about the success?

Rose: What amazes me most about Twestival’s growth is how we’ve been able to evolve and maintain a solid branch identity globally. Considering our reach and our online connection, people have been very respectful and loyal to the movement and how I have chosen to launch campaigns only once or twice a year. Something I didn’t think about while developing Twestival as a global campaign is how much it has inspired nonprofits to give social media a try or provide others the confidence to launch creative socially good campaigns utilizing new technologies.

How has social media amplified the abilities of charitable giving?

Meck: Social Media has changed charitable giving in that it has made it simple and accessible to anyone who has a cell phone.  When you look at world tragedies from Haiti to Japan, the ability to spread the word and have specific calls to action and a worldwide audience, the impact of social media is huge.

Rose: Charitable giving would not be possible without the people that dig into their pockets or align themselves with a particular cause. Social media is the vehicle that people choose to express what matters to them, influencing others to give and provides a channel for charities to show how transparent they are. There is a huge opportunity to have a daily, natural dialogue with donors through social media. It isn’t about knocking on doors anymore, it’s about gaining trust through networks of people that will support you when the ask is right. Finding that balance is often the challenge.

Why has this event grown so quickly? To what do you attribute the success?

Rose: Twitter is the obvious answer but I think it’s important to look deeper than that. Twestival is not just about tweeting or adding something to your avatar. We are asking volunteers to dedicate countless hours to organize events which their community will then physically attend and contribute to a cause to do so. That is serious engagement and it relies on a strong understanding of the different social networks and dynamics to motivate people with a simple message that they can own.

What excites you most about the localized Twestivals in 2011?

Rose: While “Twestival Local” may not sound as sexy as our Twestival Global campaign where everyone rallies around one single cause, I am most proud of the work we do locally because the impact is felt far beyond the one-day events. I believe people genuinely want to use their time, talent and resources to help a charity close to home and Twestival gives them that permission to engage with an organization that might not have the bandwidth to see how technology or social media will impact them. For me personally, this year’s campaign is all about countries experiencing the Twestival for the first time—so watching Mongolia, Saudi Arabia, Paraguay and even Tunisia putting together events with such amazing gusto really makes all the long hours worthwhile. Twestival does focus on fundraising, but at the heart of it we are all about community first.

In New York (where I live), the charity of choice is iMentor. Why work with them?

Meck: We chose iMentor because it helps children and teens in the New York area and we liked that it has both an education and technology bent to it.  In addition, we thought that we might be able to assist in recruiting mentors from the social media community.

To buy tickets to attend Twestival or find one in your local area, visit www.twestival.com

(Disclaimer: I also serve on the Young Executive Board at iMentor)