Put simply, Google's (NASDAQ:GOOG) (NASDAQ:GOOGL) search business is unmatched.

comScore puts Google's share of the U.S. desktop search market at around two-thirds, and Statcounter pegs it at over 75%. Despite Microsoft's willingness to invest billions  into Bing, their search product is barely in the same league, attracting less than 20% of search queries.

But increasingly, there's a new frontier opening up in search, a problem that if solved could create the next Google. The search giant is not blind to the opportunity, but faces competition from a host rivals.

A new search market
Google's search engine is adept at crawling websites, indexing pages for return in its search results. But Google has a major blind spot: apps. Although many apps have a web-based version, plenty don't. This makes the data they contain largely impenetrable to Google's crawlers, and not easily retrieved by its users.

Google is working to solve the problem. App indexing for Google search is a protocol developed by the search giant that allows data contained within apps to show up in its search results. By adding a few tags to their app's code, developers can allow Google's search engine to find data within their apps, and when searched for and clicked on by a user, the app will automatically open to the relevant section.

But there's a major limitation to Google's approach: Currently, it's restricted to Android apps. In other words, users of iOS (owners of Apple's iPhone and iPad) are completely left out. Google's mobile operating system is dominant, with the lion's share of the smartphone market globally, and a narrow lead in North America. But iOS is still the preferred mobile operating system for many developers, and often leads Android in most usage statistics.

Facebook's App Links
's (NASDAQ:FB) approach notably differs in that it's wholly cross platform: Not just Android and iOS, but also Windows Phone. In April, Facebook announced App Links, the first step in what could result in a project to index the mobile web.

Like Google, Facebook has developed a standard that allows mobile developers to more easily link their apps -- not to Google search, but to each other. A link sent from an App Link-enabled app will prompt the user to open the relevant app, rather than a webpage in a mobile browser. A link to a song in Spotify, for example, sent in Facebook Messenger, will send the receiver to the relevant song page within the Spotify app, rather than Spotify's website.

Ultimately, this doesn't solve the problem of searching within apps, but it's easy to imagine that it could evolve into something along those lines. Facebook's recent push into search has been overwhelming -- two years ago it announced Graph Search as its third pillar, a project that has continued to expand and intensify in recent months.

Last month, Facebook removed Bing's Internet search results from its internal search engine, replacing it with content pulled from the Facebook app itself. In the past, searching on Facebook for "New York Yankees" would've returned the team's Facebook page and some Bing web results -- now it retrieves relevant posts and status updates from friends containing the phrase "New York Yankees."

By winning over mobile developers with App Links, Facebook might be able to extend its search engine to other mobile apps, indexing them in addition to its own.

An untapped market
There are also a number of private start-ups working on the problem -- the solution may come from a company that's far from a household name. Of course, it's also possible that it's never truly solved -- many apps, particularly anonymous social networks -- may resist any attempts to be indexed.

But as the mobile web remains increasingly centered on app usage, the potential for a breakthrough is there. It's a problem that could, one day, net tech investors significant returns.

This article represents the opinion of the writer, who may disagree with the “official” recommendation position of a Motley Fool premium advisory service. We’re motley! Questioning an investing thesis -- even one of our own -- helps us all think critically about investing and make decisions that help us become smarter, happier, and richer.