It's the best possible dilemma a startup founder could face: Should you ignore the urgent emails from the high-profile venture capitalists who want to invest in your company, or the British prime minister sitting in front of you, asking for a walkthrough of your website?

Early this spring, Dale Nirvani Pfeifer chose the former option, and continued talking to the world leader instead of her potential VCs. Fortunately, the investors understood. One plane ride and three meetings later, Pfeifer had her funding--$1.7 million of it.

"I was a typical woman entrepreneur, didn't want to raise money until I was absolutely sure the idea was solid," she says now, laughing a little. "It's been an exciting few months."

Indeed, it's been a whirlwind year for the founder and CEO of GoodWorld, a fascinating--and extremely fast-growing--marriage of crowdfunding, philanthropy, and social media.

The Washington, D.C.-based startup makes it possible to give money to many charities via Twitter and Facebook. All you have to do is use the hashtag "#donate" in your social media post; then GoodWorld will contact you and ask for your credit card information, so that it can deliver your promised $10 to Oxfam or Unicef or the ALS Ice Bucket challenge (remember that?). And once you've signed up for GoodWorld's service, its payment processor keeps your information on file, so that you can make additional donations simply by using "#donate" in new Facebook and Twitter posts.

The company's growth is tremendous: Both donations and users are increasing more than 40 percent every month. About 1,000 charities are now signed up for GoodWorld's service--up from just seven at its launch a year ago--and Pfeifer says the company is on track to process more than $3 million total by May, a year after its technology came out of beta. The coming holiday season, with its attendant end-of-year surge in charitable giving and last-minute tax writeoffs, should get GoodWorld close to that goal. In fact, the company is pledging up to $1 million in matching donations in December: for every hashtag donation of at least $20 that it processes, GoodWorld will pledge an additional $1 to its customer's cause.

Pfeifer, a thoughtful yet bubbly native of New Zealand, has nurtured some impressive connections. Katharine Weymouth, the former publisher of The Washington Post, was an early investor. Kevin Roberts, the executive chairman of global advertising giant Saatchi & Saatchi, is a company adviser. More recent investors include Chris Liddell, the former CFO of Microsoft and General Motors; Raj Date, the former deputy director of the Consumer Financial Protection Bureau; Max Levchin, the co-founder of PayPal and Affirm; and Hans Morris, the former president of Visa and founder of the fintech venture firm Nyca Partners, which led GoodWorld's $1.7 million seed round--eventually.

Pfeifer developed some of these connections through her prior careers in academia and nonprofit work, but she also credits some to her D.C. incubator, 1776. It was through 1776 that she wound up in a meeting (and had her hair appear in a New York Times front-page photo) with President Obama and other local entrepreneurs. It was also through 1776 that she got invited to a breakfast meeting with David Cameron, the British prime minister.

"He's really passionate about disaster relief, and invited me over to Number 10 Downing Street," she says. Before long, "I was on a plane to London."

At the same time, Nyca was trying to set up a meeting between Pfeifer and Morris, who was also visiting England. But the delay didn't bother him too much.

"We were immediately interested, because of Dale's passion and vision to build a company that actually could do something good for the world while also making a profit," Morris said by email. "We fully expect that in a few years it will be the essential tool for raising money for disaster relief and other critical causes."

About 60 percent of people actually follow through on their social-media promises, according to Pfeifer: Since April, GoodWorld has tracked more than 20,000 #donate pledges on Facebook and Twitter worth more than $500,000, from which it's collected more than $300,000. The average donation has held steady at slightly under $30, though GoodWorld also makes repeat donation via social media easier. If, last summer, you told Facebook that you'd pledge $100 to fighting Lou Gehrig's disease as a justification for dumping a bucket of ice water on your head, Pfeifer's company now has access to your credit card details. So this summer, if fighting diabetes by, say, entering hot-dog-eating contests becomes the next viral meme, tweeting about it with the #donate hashtag could automatically send your money on its way.

GoodWorld sits somewhere between traditional payment processing (it pays a fee to Stripe, which collects its credit card payments) and standalone, charity-minded crowdfunding sites like Indiegogo, CrowdRise, and Tilt. GoodWorld is more behind the scenes than Indiegogo--it's essentially a vendor to charities rather than a self-supporting crowdfunding site. It charges non-profits between 7 and 8 percent, including 2.2 to 3.2 percent for credit card processing, which is on the low end of what most crowdfunding sites charge.

It may be ironic, of course, that a woman who's built a technology company for non-profits is doing so in the for-profit sector. But Pfeifer has several arguments for why she's not doing this as a charitable endeavor--and ones that I've heard from many socially minded entrepreneurs of late, including Malala Fund co-founder Shiza Shahid, Dell and former United Nations entrepreneur-in-residence Elizabeth Gore, and Kind founder Daniel Lubetzky.

"Being a for-profit company has allowed us to attract this incredible cadre of investors, and bring their financial acumen to the company. Their connections, their support, and having them really push us and keep us accountable has been incredibly helpful," Pfeifer says, adding that her funding has allowed GoodWorld to staff up quickly: "If it was a nonprofit and I was going out and asking for grants, it would have been hard to pull together the kind of capital to grow and scale this business."