Google announced the introduction of Search Ads via AdWords on the Google Play Store.
Google said, "Search Ads on Google Play will begin to roll out today to all advertisers and developers who use Search app install campaigns on AdWords."
So now when you are searching for apps in Google Play, Google may show you ads that look like this:
This is how advertisers can set up search ads within the AdWords interface:
Google says they have over 1 billion people on Android devices in more than 190 countries. So the reach and the search volume should be there.
Forum discussion at Google+.