Flurry, the San Francisco-based analytics and monetization company, is launching a new advertising service that is designed to bring users back to apps they’ve already downloaded. The company said after tracking retention through 110,000 apps across its network, it found that the critical problem for developers isn’t discovery, but rather re-engaging users from an existing installed base.

If you look at the chart above, an app might retain just under 40 percent of their users after the first month. The percentage drops to 14 percent by the sixth month and to 4 percent at the year’s mark.

Flurry argues that that classic approach of doing a “burst” campaign by buying a sufficient number of ads or installs to drive an app up the charts upon launch is not always the most effective for most developers — especially considering that it’s becoming more expensive with each passing month due to rising competition.

“Always trying to rank high, as a tactic, is not only untargeted and expensive, but also suffers from diminishing returns,” wrote the company’s vice president of marketing Peter Farago in a blog post. “First, the bar required to make the top 25 keeps rising, as the installed base of consumers grows and more apps compete for a fixed number of top spots.”

Secondly, ranking high doesn’t bring users who have already installed an app back into it.

So the company’s launching new interstitial ads that target users a developer already has, encouraging them to come back to their apps. Flurry has its own ID scheme to tell which users have what apps already. Since Apple is planning deprecate its unique device IDs out of privacy concerns, which many ad networks were using to target consumers, Flurry has rolled its own identifier.

All install networks like Flurry and its rivals Tapjoy, W3i and others are hunting for revenue streams that can make up for the loss of offer walls, which were a lucrative way of driving downloads for developers up until April of this year when Apple cracked down on the practice.

Tapjoy has gone deep into Android, replicating its network on Google’s platform, and it recently launched a mobile web-based gaming platform that will allow the company to own a direct relationship with its consumers. W3i has done a free-app-a-day scheme called AppAllStar. Flurry has done incentivized video ads, which give gamers free virtual currency if they watch videos (usually game trailers) for other apps.

Launching a re-engagement ad product, which doesn’t clash with Apple’s recent policy changes around incentivized downloads, will give Flurry a way to re-engage its most valuable customers: the app developers who were early and accumulated large footprints on the iOS platform.