I don't think I would add anything to Sean's pyramid but I do have my own approach to things that essentially breaks it down a bit more to a granular approach.
1. Find users who've had success
If you're lucky to have 100-1000 users, I'm hoping you can identify 5-20 of them that love your product or had success. If so, then study them. I always suggest trying to understand what "path" they took when signing up for your product, in what order, and see if there's commonalities. Find them, then change the way you introduce (onboarding) your product to new users so they all experience the "a ha" moment those users discovered.
2. Test the size of the market
The biggest challenge I see with startups is that they spend 99% of their time iterating around the product, and 1% thinking about the market. It's called product / market fit - so spend time understanding if you're product actually addresses the needs of the market. If not, maybe try a different market and see if it sticks. Many times it's not the product, it's the market you're trying to serve that doesn't have a real "must have" desire.
3. Identify your growth engine.
Eric Ries described it best in his book The Lean Startup, but Lars does a good job recapping it here: http://larslofgren.com/marketingbasics/the-three-engines-of-growth-with-eric-ries ... don't fool yourself in believing that you have some new / unique distribution approach. Find the growth engine that describes you, and start iterating around those user flows.
So in summary, not that I would add anything, but I would elaborate more on the mechanics of growth hacking then just talk high level at 30,000 feet.
I would add a layer beneath "Product/Market Fit" called "Seed Growth," and here's why:
Sean Ellis' Pyramid is awesome, but you'll never know that you have (or don't have) product/market fit unless someone is already using your product. But where do these people come from? For instance, Sean recommends sending questionnaires to your existing users asking them how disappointed they would be if your product was no longer available, as a way to determine if product/market fit has been achieved. However, this begs the question: where did those people come from who you sent the survey to?
This is where "Seed Growth" comes into play. You need to grow the initial user base, from nothing to something, before you can determine product/market fit and move on to the other levels of the pyramid.
There are a number of ways to find this initial growth, but I would recommend the relevant parts of Paul Graham's famous essay as a starting point: http://paulgraham.com/ds.html and I would recommend watching Growth Hacker TV (www.growthhacker.tv) as another source for growth tactics.
You can watch my episode with Sean Ellis here: https://www.growthhacker.tv/sean-ellis
I would add at the bottom "idea generation" and the "product/market fit" sentence will also be vertical all along the pyramid.