PARIS - They set off by train, foot, bike, plane and even scooter but however they move, and whatever route they take, these 21st century travellers share a common desire: to make the planet a better place.

Some want to raise money for a worthy cause. Some want to build something with their hands. Others want to share their ideas.

Take the Colas family from Paris, for instance. In 2010, they decided to take off on a world tour, mixing adventure with a specific goal.

"We wanted to build a school in Burkina Faso," said Mr Frederic Colas, a 45-year-old businessman.

He had come up with the idea of zeroing in on the central African country after meeting a volunteer from La Voix de l'Enfant, an association involved in the region.

To make it happen, the Colas created their own website, We Like The World, and began to tap their social contacts.

"The result was a network of 1,000 people - mostly friends of Facebook friends - who helped us," said Mr Colas.

They were also hosted by 52 families in 17 countries. For each free night in a local home, the Colas pledged US$100 (S$125) for the school, while new fans on their Facebook page pledged US$1 each.

After 12 months of travel, they had collected US$23,000 - a sum which was more than matched by gifts from sponsors that included French telephone company Orange and Stade de France, the giant stadium outside Paris.

In total, the family managed to raise US$65,000 to build the school, which now houses 200 happy schoolchildren.

The Colas are among a growing tribe of backpack philanthropists who have helped to make the world a better place - while on holiday.

There's Canadian Rick Hansen, an early pioneer in the scene. In 1985, Mr Hansen, a paraplegic, set out on the Man In Motion World Tour to circumnavigate the world in his wheelchair.

Over the next two years, he would cover more than 40,000km and 34 countries to raise awareness for spinal cord injuries, raising US$26 million in the process.

There is Mr Ludovic Hubler, who spent five years hitch-hiking around the world. Since coming back in 2008, he has been working on Travel With A Mission, a website that aims to develop engaged tourism.

And there is Mr Riaan Manser, who became the first person to circumvent Africa on a bicycle and kayak around Iceland and Madagascar. The adventurer has raised money for the No Food For Lazy Man Trust, giving disadvantaged children access to sports equipment while teaching them to contribute to their community.

So what sets people off on such socially conscious world tours?

For Mrs Estelle and Mr Frederic Colas, who have a daughter, it was the realisation that they were not going to have another baby.

"We asked ourselves what could we do that we couldn't do if we had an infant," said Mr Colas.

Backpack philanthropists, however, have found that this type of travel can be a real challenge.

Many have found that preparing for a trip, launching it and executing it can be an education in itself. By their accounts, the advance work can take anything from six months to two years, and require organisation, determination and conviction - all skills that are highly prized in the working world.

Mr Matthieu Dardaillon and Mr Jonas Guyot, for instance, spent a year and a half on preparations in Britain, France and Austria before they could start their Destination Changemakers trip to rally support for social entrepreneurs in India, the Philippines and Senegal.

And Mr Hugues Renou, co-founder of Trott My World, was surprised to find out how hard he had to work as he travelled the world by foot scooter.

"Just the meetings with entrepreneurs and our reports for the blog take up 75 per cent of our time," he said via Skype from Argentina.

The work continues after they return. Many travellers take time off to spread the word about their trip and what they have accomplished as they hold conferences, write books and upload their videos. As a result, some end up inspiring others to follow in their footsteps.

One of Mr Frederic Colas' clients, for instance, left in April to do a second edition of We Like The World. Ms Irene Meister's trip will raise money to help underprivileged girls in Angkor, Cambodia.

Some of her friends are planning to join her, even if only for a few weeks.

"I do hope to inspire people as the Colas inspired me," she said.