One of the most rewarding and cost-effective marketing campaigns I’ve ever done was one in which the stakeholders carried the message. I created a campaign that asked hospital donors and the public to send in their stories about why they gave to the hospital. And then I asked people to go online to vote for the top story. We received 30 stories and 500 people went online to vote. Web traffic doubled, online giving went up. More importantly, our donors were engaged.

That technique is called word of mouth marketing, and more and more it is becoming an essential item in every marketing toolbox.

The technical definition of word of mouth marketing is a “strategy, supported by research and technology, which encourages consumers to dialogue about products and services,” according to PQ Media, a US research company which measures its use. In other words, it is about creating “buzz” — people talking to people about your stuff.

This, as you already know, isn’t new. Buzz has been around for centuries. Word of mouth marketing simply recognizes and amplifies a pre-existing phenomenon — people will talk about something that interests them to others they know. Word of mouth marketing doesn’t create that buzz, it just makes it work with a marketing objective in mind. In other words, the voice still belongs to the customer. Word of mouth marketing simply harnesses that to deliver a marketing message. The key is to listen, facilitate and encourage the sharing of information.

Authenticity is the cornerstone of word of mouth. Real buzz can’t be faked or manufactured. Just ask Sony Pictures. In 2001, ads for films including Hollow Man and A Knight’s Tale quoted positive praise from a reviewer called David Manning, who was exposed as being invented. Sony temporarily suspended two employees and wound up paying a hefty fine. Worse, their credibility was tarnished.

Word of mouth works in a number of ways. First and foremost, it encourages communications. Today, marketing is all about conversations. The more people talk, the more engaged they are. It also works because it creates a sense of community. In our wired and increasingly wireless world, people are beginning to think in terms of tribes. A shared experience, like a word of mouth campaign, can fuel this.

Another factor is the way this technique identifies and empowers influencers in your stakeholder community. Its very nature attracts the truest believers and strongest advocates.

The impact of word of mouth also runs both ways. Your stakeholders learn about you, but you also learn about them. A campaign like this promotes listening. Perhaps one of the best things about word of mouth is it is easy to measure. Since most of the tools involved are online offerings, metrics are superior to many other forms of marketing.

As a marketing technique, word of mouth is cost-effective. It doesn’t take much to start a campaign. Many involve simply a good idea and existing social media platforms. There is some legwork involved, especially in the research needed at the front end. But there are also savings, because much of the content is user-generated. It is also a multi-platform technique that can be used across most channels, including mobile devices.

The result is that word of mouth marketing is growing at a time when many other marketing tools are shrinking. According to PQ Media’s Word-of-Mouth Marketing Forecast 2009-2013, spending on U.S. word of mouth marketing increased 14.2% to $1.54 billion in 2008. Total spending is expected to increase 10.2% to $1.70 billion in 2009 and grow by 14.5% during the 2008-2013 period, reaching $3.04 billion.

The power behind word of mouth has much to do with the changing marketing landscape. Media consumption has been transformed by the Internet, the social media revolution and, lately, the explosion in mobile devices, like smartphones. The result has been serious fragmentation, which has made it more difficult to reach their target audiences. People read fewer newspapers and watch fewer TV channels and spend more time online or playing things like video games. This is especially so with younger generations. Word of mouth fits easily into the new way of marketing. It is online, conversation-based and youth-friendly.

In the Harvard Business Review, McKinsey & Co. strategy consultant Renée Dye, found that two-thirds of the US economy is at least partially effected by “buzz”. It is a myth that only outrageous or edgy products are buzz-worthy. In fact, most things are. She found that all something needed to be “buzzable”, is a uniqueness and visibility. The best “buzz-starters”, she said, were usually an organization’s best customers. The only major challenge in creating buzz was timing — buzz has to catch the wave at just the right time.

But will it work for a nonprofit? The answer, according to the Word of Mouth Marketing Association in the US, is yes. They point to the New Jersey State Library which ran a word of mouth campaign called the SuperLibrarian Video and Comic Contest in 2008. The goal was to create some buzz for the local library among younger audiences. The contest yielded 40 submissions. The voting process to pick the winner generated 17,000 votes. Analysis showed that most of the votes were generated by a small number of teenage influencers who in turn engaged friends, family and community in the project. Since it was primarily based on existing channels such as websites and YouTube, the costs amounted to just a few posters and some prizes.

So, how can you do a word of mouth marketing campaign? Start by trying to identify your existing influencers, especially those who have extensive social networks (online or offline). Do some research with them to find out what kind of campaign would be of interest.

Remember, it has to be something they “do” as well as communicate to others. Get a few suggestions and test them. At the same time, start routinely capturing online contact information about your stakeholders — email, websites, blogs, Facebook, LinkedIn, YouTube, etc. When you want to start a word of mouth campaign, you’ll need this to get started. Over the long haul, remember to encourage recipients of your email messages to forward the mailings to others. And make sure you routinely get your stakeholders involved in communicating to others through things such as sending a letter to the newspaper or a local politician. The more active they are, the better.

Based on my experience, likely the biggest challenge you will face when embarking on a word of mouth marketing campaign is the scepticism of your colleagues. Many simply won’t get it. Do research at the beginning of the project that shows how receptive your stakeholders will be to the campaign. Try it on a small scale, if necessary. But don’t let them dissuade you. Word of mouth is here to stay and it’s too powerful to ignore.

John Suart is a marketing and communications expert with an MBA who specializes in nonprofits. His blog, the nonprofit Marketer, has a host of useful tips and advice on everything from budgeting to branding.