Pinterest, the content sharing site that allows users to “pin” images and videos to their digital “pinboard,” is currently one of the most popular social media websites on the Internet.  As of October 2013, just three years after the launch of the site, Pinterest had over 70 million users, including 500,000 business accounts.

The site currently attracts nearly 2.5 billion monthly page views and about five million daily article pins. How in the world did it get so popular so quickly? The story behind Pinterest’s growth is a fascinating one, mainly because it is one of the most brilliant and successful examples of growth hacking ever used by a social media company.

The idea behind Pinterest was conceived around 2008 by Ben Silbermann, a young, soft-spoken 20-something from Des Moines, Iowa. Silbermann always wanted to be an entrepreneur and growing up, his role models were innovators like Walt Disney and Steve Jobs. Out of college, Silbermann became a consultant in the tech division of a company, and he found himself fascinated by websites like TechCrunch, which contained technology news and numbers. Silerbmann moved to Silicon Valley and took a job at Google.

Being surrounded by other tech inventors, he was inspired to come up with an idea for a technology company of his own. His first company was called Tote, a catalog app for the iPhone that he invented with a fellow tech friend based in New York. However, this app came out in 2008 when the economy had collapsed, so Silbermann found it impossible to attract investors.

As he struggled to get Tote off the ground, he became distracted by another idea, a sort of online display of a person’s favorite items and collections. Silbermann had collected bugs as a child, and he thought that sharing your collections was a great way to get to know another person. He approached his friend Evan Sharp with the idea, who also thought it would be tremendous for a website. Sharp came up with the idea of having a grid-based website (which Pinterest still uses), and in January 2010, Sharp and Silbermann pinned the first pin onto the first Pinterest board.

Some might be tempted to say that the rest is history, since Pinterest had an immensely successful reception across the board (no pun intended). And, indeed, Pinterest became popular with users right away. For example, a woman named Victoria helped Silbermann and Sharp organize a program called “Pin it Forward,” which was like a chain letter where users circulated different pinboards about what their homes meant to them.

By August 2010, Pinterest had attracted 40,000 unique visitors. However, what led to the immense success that Pinterest has found today is not simply the appeal of its site, although it is immensely user-friendly, attractive and useful. In reality, Pinterest has reached its current heights because it has implemented some of the very smartest and best growth-hacking techniques, which have allowed it to be shared between users and grow bigger on its own.

Unlike some of the other biggest sites on the Internet today, Pinterest did not launch with an immense amount of hype behind it. Instead, it was a homegrown program launched by some passionate thinkers who ultimately had to go back and incorporate some smart growth-hacking methods into the program once it had already been set free.

One of the most important ways Pinterest incorporated growth hacking into its marketing scheme is its signup process. In order to join Pinterest, users can’t just visit the website and join. Instead, they have to request an invitation to the site, making it feel like an exclusive club to which you actually want to belong. People always want to be a part of something that they’re not initially included in, right? After new users request an invitation, they receive one by email a few days later, making it feel like they have been approved for a special offer or accepted into an exclusive group.

This makes Pinterest seem like a privilege to use right off the bat, enhancing its reputation as a site that people covet. The invitation email uses strategic wording and content, as well, to help bolster its image, calling Pinterest a small community and offering rules about how to behave while there.

In addition to its joining process, one of the Pinterest’s other most successful growth-hacking techniques is its initial automatic link with Facebook. Once users join the community, Pinterest instantly gives them the option to sign up with their Facebook account, making it easy for users to start using the site without jumping through a million hoops and more likely that they’ll start using the site right away as opposed to putting off use because of all the bureaucratic stuff. This also connects users to their Facebook friends immediately, so that they don’t start with an empty social media profile page. Rather, Pinterest’s Facebook connection allows new users to see a page full of people they know, which is an incentive to keep using and exploring further.

Another growth-hacking technique that happens when a user first starts using Pinterest is its interest survey. Pinterest shows users a variety of images and asks which ones appeal to them. Based on a user’s responses, it follows some related and popular boards that match the user’s choices, automatically generating content and information that makes users feel like they are already part of a community and in turn, encourages them to explore the site further.

Pinterest’s growth hacks go beyond simply what it requires or offers a user right at the get-go. In fact, one of Pinterest’s principal growth hacks is its user interface (UI), which allows a user to perform almost every possible Pinterest function from their one, main page. Not only can users comment, re-pin or check out another board from their main feed, but they can also follow new friends, check out the website from which a pin came, share a pin through other social media networks, or edit their own profile or pinboards.

The easy usability of Pinterest makes it extremely popular with users, not only through word of mouth, but also through the direct ability to share the site via simple buttons that connect to email and social media networks. Another element of Pinterest’s design that has helped make it so popular is its infinite scrollability.  Users can continuously scroll down their feed without ever reaching bottom and having to click a new button to get more information.  This allows for ease of use, and even encourages losing track of time while browsing, ultimately upping time spent on the page and in turn, boosting its SEO ranking.

The growth hackers behind Pinterest also took advantage of email in order to help it go viral. Every function and action on Pinterest is linked with an email alert, which, when sent to users, keeps them up to date on what’s happening on the site and reminds them to go and engage themselves. While emails are optional, the immediate opt-in feature helps keep users engaged and interested with very little effort on the part of either the user or the company.

Ultimately, Pinterest is such a success story because it combines two things, a really great product with an equally great scheme for viral marketing. Its growth hackers have done an incredible job of attracting new customers and keeping them engaged, which is important for growing the company and attracting more users.

But the product is also one that is extremely well-designed and useful for both individuals and companies. Today, Pinterest is used by companies because it has a 50 percent higher conversion rate than any other site that directs people to products, and Pinterest users regularly spend more money, more often than any of the other top four social media sites (Facebook, Twitter, YouTube, Google+). In fact, Pinterest currently generates four times more revenue per click than Twitter does and nearly three times more than Facebook.

If you’re an entrepreneur who believes in your product, and you are looking to grow your business virally online, you should pay heed to the strategy behind Pinterest’s growth. Not only has it created a popular site that is entertaining and helpful for promoting social interaction, but one that has also helped changed the way business is conducted online.