Here's The Number Google Should Worry About When Facebook Reports Its Earnings Tomorrow

NrkbetaGoogle sales boss Nikesh AroraFacebook reports its third quarter financial results tomorrow.

We'll have live coverage beginning just before 4 P.M. eastern.

There's one number that Google sales boss Nikesh Arora should be on the lookout for: the number of mobile app developers who bought Facebook ads promoting their apps.

Facebook has an mobile ad product where app developers pay Facebook every time a user installs their app.

In the first quarter, 3,800 developers bought install apps. In the second quarter, the number increased to 8400. This quarter, the number could hit 20,000 or more.

That number's rapid growth signifies how, as personal computing shifts from desktop to mobile, Google's position as the way for consumers to discovers businesses through the Internet is weakening.

On the desktop, the way a business gets a user's attention is by building a website and then optimizing it for Google search and promoting it with Google ads.

On mobile, the way a business gets a user's attention is by building an app, optimizing it for the Google and Apple app stores, and, increasingly, promoting it with Facebook ads.

Facebook has a long way to go before this business scales to anything close to approaching Google's. While Facebook approaches 20,000 mobile app install advertisers, analysts say Google has at least 1.5 million Web advertisers.

But Facebook's app install ads are a very new product. Q1 was its first quarter.

And while the desktop Web is very mature, mobile usage, and Facebook's share of it continues to grow.

It's hard to believe, but consumer usage of Facebook's mobile apps actually continues to accelerate.

JP Morgan analyst Doug Anmuth sent out a note this morning reporting that growth in Facebook's total U.S. minutes accelerated to 34% year-over-year in September, up from 33% year-over-year in August and up even furhter from 22% year-over-year in July 2013.