Growth hacking is not just how to grow your customer base, but how to escalate those customers into highly active, often revenue generating, customers. It’s the ability to create that magical combination of a single action that triggers an action from a prospective user (such as the “like” or tweet) which directly matches an action that naturally encourages the network effects (like sharing, linking, signing up, upgrading etc. ). So a hack that moves customers from free to paying in a freemium model, may have more impact to a business than something that just invites new users.

These are some of the most ingenious growth hacking strategies that attracted millions of users within a short period of time.

1. You’ve just been tagged in a photo on Facebook. The  CTR on an e-mail notification like this could be in excess of 75%, and likely within minutes of receiving it. An email like this can suck hours away from you before you know it, which is the reason Facebook has such huge engagement numbers. But in the end, nothing gets people back into Facebook better than being mentioned in a comment  or better still, getting tagged in a photo, and at over 350 Million New Photos Each Day, that is outstanding.

2. Invite a friend and get an additional 500MB of storage (Dropbox). Dropbox,Box, and other revolutionaries in the world of cloud storage figured out quickly that free storage (whether used or not) was a great trigger to invite friends. When they started offering 500MB for a referral, what feels like a huge amount (but is really quite cheap to provide), it felt like a ton of value to share. This worked to help Dropbox grow from 100,000 users to 4,000,000 in under two years.

3. The Pinterest infinite scroll. Once Pinterest got imaging right with that high quality imagery, people couldn’t get enough. The infinite scroll that allowed people to just keep seeing more and more by scrolling down the screen created a new visual hunger. They introduced each user to hundreds of other pins, feeds, and ideas in minutes, more so than any “email your friends” hack ever could.

Again, upon signing up for Pinterest you are automatically following a select group of high quality users. This in turn helped alleviate the cold-start problem, where you have to go looking around the site to find boards and people to follow. Instead they presented a sampling of high quality content immediately filling your feed.

4. This coupon is only valid if you invite 1000 friends (Groupon). Groupon was one of the fastest growing companies in the world for good reason.  – their core product required sharing with lots of friends to turn on. The incentive here is to invite everyone who does just about everything. bout ANYTHING, not just a few who do a niche thing (like Candy Crush to gamers). It’s the same reason merchants are crazy enough to offer 70%+ off even if it’s not good for business  – it reaches more users faster than any marketing to date, hands down.

5. Cross-posting (Instagram): When you shared an Instagram image on Facebook or Twitter, you were taken to an Instagram page with the photo and a very strong call to action to download the app. This was especially true if you were on iPhone in the early days before they had an Android app. All you could do is view the image and download the app.

6. Get your free email at Hotmail [link]:– this is old school Web 1.0 growth hacking. Hotmail was a provider of free email. At the end of your email message, they automatically added the signature ‘Get your free email at Hotmail [link]’. Within hours of this their growth took the shape of the classic hockey stick growth, going from 3000 users a day to 1 million users in 6 months, to 2 million 5 weeks after and to 12 million users in 1.5 years.

7. Candy Crush (So what happens when you die?). This addictive game is absolutely crushing it right now. Initially you could do one of 3 things when you die:

  1. wait until the reset timer runs out and you can play again in 30 minutes
  2. pay and you get to play again right away
  3. sell out your friends by inviting them to ‘help’ you

8. The Craigslist factor (AirBNB). AirBNB leveraged Craigslist, a platform with millions of users looking for accommodations, to increase their user base substantially. When you are filling out the form to list your bedroom on AirBNB they give you the option to also post the listing to Craigslist, so that it will show up there also, creating inbound links for you and for AirBNB as a platform.  AirBNB  had to reverse engineer how Craiglist’s forms work, and then make their product compatible, without ever having access to the Craigslist codebase.

9. Gmail invitation-only beta release:  Gmail initially was available only through invites. This gave an air of exclusivity to the product and people were in fact asking for invites to others.

10. Paypal’s friend referral bounty: By paying $10 cash to each new customer and $10 to the customer who referred them, Paypal was able to hack early growth to tens of millions of users before no longer offering the bonus.

11. Mailbox waiting list. By creating an incredibly compelling launch video combined with a very cool interface that showed users how many other users were in front of them on the app’s waiting list, mailbox created a large amount of social chatter and blog attention. Within six weeks, Mailbox had a million users signed up and eagerly waiting for the service.

12. content/seo strategy. Mint focused on building out a unique personal finance blog, very content-rich, that spoke to a young professional crowd that we felt was being neglected. Eventually the blog became #1 in personal finance, and drove traffic to the app. The infographics and popular articles became regular hits on Digg, Reddit, etc.

13. Linkedin relied on power users. They seeded the product with well connected influencers, and cultivated an ‘inspirational brand’, which later drew in the mainstream. This is remarkably similar to what Quora did.