Blake makes great points about going viral. That is not something that is planned, but you can do several things in order to give you app a chance for this type of exposure. Since most of those 24,000 people that like your FB page do not see your posts (because that's how FB works), I would start there. Promote you posts through FB ads to reach that audience first. They have already showed an interest in your product. You can spend as little or as much as your budget allows. Driving app downloads through FB can be a challenge, considering paying .50 a download can be difficult to stomach for a free app. But to get started and get some traction, it could be the best route.

After leveraging those you already have interested, you can look at other avenues (twitter, instagram, etc). I would also consider Product Hunt. A site I created recently was featured on Product Hunt after being hunted by a top influencer on the platform. Be sure to research Product Hunt thoroughly, though. It does you little good if you aren't featured and there is a process to follow for a chance at that.