In San Francisco, where Twitter is based, gathering a crowd was the easy part. In a city where a gaggle of young, tech-savvy hipsters will turn out to watch paint dry, Twestival was basically on home territory.

Regardless, the local organisers had brought together a mixed crowd of more than 400 people, who dutifully converged on a downtown club to meet each other and raise money.

With their usernames scribbled onto badges, the attendees mingled with each other and got to know the faces behind the tweets.

"I'm relatively new to Twitter – I'd say I've been twittering for six months," said San Francisco resident Brit Pinkey, who had been told about Twestival by a friend. "It's cool watching people utilise it and doing positive things with it."

Upstairs, where a silent auction was taking place to raise extra cash for charity, a row of banquettes was filled by twitterers who sat tapping feverishly on their BlackBerrys and iPhones. Downstairs the crowd was entertained by live music and the prospect of freebies donated by local companies.

"I heard about Twestival a month or so ago," said San Jose resident Derek Overby, who works for a real estate website. "Some guys I know in London were going to the London Twestival … so I went to the site and found out that they were doing it in 200 cities."

His verdict on the evening?

"Awesome," he said. "I can't believe how many people have shown up."

Not surprisingly, given the proximity to Twitter's HQ, many of the team behind the site were in attendance – including chief executive Ev Williams and co-founder Biz Stone. And although it played a role in helping the event happen, Stone told the Guardian that the credit was due to the organisers, not Twitter itself.

"I've been emailing … asking how we can help," he said. "But really it's been all them, it's been all Amanda [Rose]. We've just helped promote it."

He added that he was pleased that users of the website could come together and do something positive, rather than simply socialise with each other over the internet.

"One of the things that this helps hammer home for us is that Twitter isn't about the triumph of technology … it's about people," he said. "If we can provide a simple enough tool to help people do stuff like this, then we're really happy."