Based on what I can glean from your description of the situation, my assessment is your company is hemorrhaging talent because it doesn't stand for anything and therefore no longer engenders any loyalty. You've achieved the what and the how but you haven't yet found the why for accomplishing either.
You say your company is number one in your industry. Getting to number one was the likely incentive for the people who said yes and joined up early in your company's life. They took on the risks and other pitfalls of working at a startup because it afforded them an opportunity to achieve a trophy other established companies could not offer.
But that was last season. What new championship is your company offering to these top performers this season?
Top leaders forge a company culture: a reason to win. The culture is what gives members of a team something to go after beyond material compensation. Without culture -- without a reason to earn a big win for the cause (instead of just the numbers) -- there's nothing unique on offer, nothing to sacrifice for. It's the difference between being having a task and having a purpose; between having something to do and having a passion to pursue; between repeating the same things and making a difference in the world.
I know that may sound very "motivational-speakery", but all human endeavor really comes down to fulfillment. We do that which we think will bring us satisfaction. Money only motivates up to a point. If all you have to offer is more cash, there's always someone else who can out-spend you for the specific slice of talent that matters more to them, and your company gets carved up over time.
I recommend the work of

• Simon Sinek -- TED talk
• Daniel Pink -- TED talk / RSA animate video
• Tony Hsieh -- Harvard Business Review article

as primers.
Some practical advice:

1. Who is responsible for retention? Unless certain individuals are tasked with and actually empowered to turn the issue around, it's spread will only accelerate throughout the company. Eventually your innovative start-up will be hollowed out at its core and replaced from the inside with a safe, complacent middle-of-the-road staff.
2. Who is setting the company culture? Every company has a culture, but a good culture is only crafted by intention from the top with purposeful leadership. Somebody has to say "This is what our company is, and this is what it isn't," and that person who says that needs to carry enough weight and authority to make those statements stick.

Both of these areas of responsibility are mission-critical, full-time work.

Based on what I can glean from your description of the situation, my assessment is your company is hemorrhaging talent because it doesn't stand for anything and therefore no longer engenders any loyalty. You've achieved the what and the how but you haven't yet found the why for accomplishing either.

You say your company is number one in your industry. Getting to number one was the likely incentive for the people who said yes and joined up early in your company's life. They took on the risks and other pitfalls of working at a startup because it afforded them an opportunity to achieve a trophy other established companies could not offer.
But that was last season. What new championship is your company offering to these top performers this season?

Top leaders forge a company culture: a reason to win. The culture is what gives members of a team something to go after beyond material compensation. Without culture -- without a reason to earn a big win for the cause (instead of just the numbers) -- there's nothing unique on offer, nothing to sacrifice for. It's the difference between being having a task and having a purpose; between having something to do and having a passion to pursue; between repeating the same things and making a difference in the world.

I know that may sound very "motivational-speakery", but all human endeavor really comes down to fulfillment. We do that which we think will bring us satisfaction. Money only motivates up to a point. If all you have to offer is more cash, there's always someone else who can out-spend you for the specific slice of talent that matters more to them, and your company gets carved up over time.

I recommend the work of

• Simon Sinek -- TED talk
• Daniel Pink -- TED talk / RSA animate video
• Tony Hsieh -- Harvard Business Review article

as primers.

Some practical advice:

1. Who is responsible for retention? Unless certain individuals are tasked with and actually empowered to turn the issue around, it's spread will only accelerate throughout the company. Eventually your innovative start-up will be hollowed out at its core and replaced from the inside with a safe, complacent middle-of-the-road staff.
2. Who is setting the company culture? Every company has a culture, but a good culture is only crafted by intention from the top with purposeful leadership. Somebody has to say "This is what our company is, and this is what it isn't," and that person who says that needs to carry enough weight and authority to make those statements stick.

Both of these areas of responsibility are mission-critical, full-time work.