Awesome to hear, congrats on making it this far!
One thing I'd suggest is taking a look at the pre-launch strategy of the shaving company, Harry's. You can find details here: http://fourhourworkweek.com/2014/07/21/harrys-prelaunchr-email/
Basically, what they did was gameify their referral program to entice early adopters to bring their friends in. At each level - 5 people referred, 20 people, etc. - there was an item that got unlocked for the referrer. You could offer 5% off a ride for five people referred, 20% off for 20 people referred, etc.
Harry's co-founder, Jeff Raider, spoke about the strategy and its effectiveness on Hubspot's Growth Show podcast: http://www.hubspot.com/podcast (The podcast is excellent, and each episode contains at least two or three great insights into growing a company; can't recommend it highly enough.)
The last thing I'll is this: "Growth hacking" should be considered a dirty term. I'm sure you've heard this before, but growth isn't something that you should consider hackable, at least not for the long-term. Growth is a reflection of your company's focus on the product. Alex Schultz, an early member of the Facebook growth team (the Navy Seals of the startup growth world), gives a really great lecture about this concept here: http://startupclass.samaltman.com/courses/lec06/
Hope the above is somewhat helpful and that the lack of coffee isn't affecting my ability to communicate too adversely. Looking forward to hearing about the highs and lows of your journey. Best of luck, amigo.