Want more users to download your new app? There's... no app for that.

At least, there isn't one yet, and if the latest download numbers are any indication, users probably won't download it anyway. According to comScore's latest mobile app report, an average of nearly two-thirds (65.5 percent) of U.S. smartphone users have downloaded a grand total of zero apps each month.

The breakdown of the remaining third of Americans who downloaded at least one app is as follows:

comScore

Though the downloading landscape seems bleak, users are engaging with apps more than ever, the report states. Mobile activity now trumps desktop activity 60 percent to 40 percent, with mobile apps accounting for 52 percent of the former. 

It's largely thanks to social networking platforms, mobile games, and radio apps, which in total account for nearly half of all app activity:

comScore

In addition, the biggest brands—Facebook, Google, Apple, Yahoo, Amazon, and eBay—make up for nine of the top 10 most used apps. And that's likely the reason why people don't feel the need to download new ones: Established brands continue to improve their products with new versions, and have already learned the lesson that newer products (Facebook Paper, for example) don't have the same pull.

All in all, the discrepancy between app usage and app downloads simply means a tougher challenge for advertisers looking to capitalize on the burgeoning market.

"Like any emerging advertising medium, it takes time for the ad buying and selling infrastructure to develop," the comScore report concluded. "The good news is that, throughout the history of media, dollars eventually follow eyeballs, which means that the future of the mobile app economy is very bright."