Google has announced a new campaign to cater to Mobile app installs on Adwords. Starting July 1st the New Google Search Network only - Mobile app installs campaign will replace Search Network only campaigns with ad app install ads.
"As part of our ongoing effort to improve app promotion features in AdWords, we are making some changes to mobile app install ads (also known as click-to-download ads) on the Search Network. Starting July 1, 2015, we will support the creation of app install ads for the Search Network only in the Search Network only - Mobile app installs campaign type. In addition, app install ads created for the Search Network outside of this campaign type will stop running in July 2015. This includes any app install ads running together with website text ads in a Search Network only - All features campaign." - Google Developers Blog
To ensure uninterrupted serving of app install ads on the Search Network, make sure you move them to a Search Network only - Mobile App installs campaign before July 1, 2015.