I will just add that if you are seeing an "Open" option in the play store that the app is installed on your device and depending on the device manufacturer, for example Samsung, if the app is in a folder the icon won't appear in the app drawer it appears inside of the folder in the app drawer. Earlier this evening I ran into the same thing looking for an app I thought I had. Meanwhile you can find the app by using the search feature in the app drawer, but you'll have to find the folder on your own.