In an ideal world you can drive downloads through in-app advertising/media buying. I would consider putting together a small budget for Facebook Ads for Apps (nearly 60% of all FB traffic is mobile and the average click cost is $.27 per). Then you can roll-up a look-alike campaign to target specific potential users nearing the profile similarity of your current power users (this is all done through a pretty easy-to-use portal within Facebook ads). FB certainly isn't the only platform, but I would argue one of the easiest to activate and scale.

Is your app free to play with IAP or is there a download cost? You may want to consider sending free memberships to bloggers or other connectors in the gaming arena to get their input so they can share with their engaged audiences via social media etc.

There are a myriad of ways and means to drive downloads towards your app - some are costly, others only require sweat equity. You should find tactics that match your target audience and your games brand messaging so your request comes across as authentic and to the right potential group of people. Feel free to reach out if you'd like to connect and explore other ideas. Best of luck!