The application-driven systems on mobile devices pose another threat because they could allow Zynga and other services to offer their own mobile apps to bypass Facebook and connect directly with users.
The rise of mobile devices also opens up an opportunity for Google to expand the audience of Plus, its social networking alternative to Facebook. Although it hasn't done so yet, Google could make Plus part of the Android operating system that runs 250 million smartphones and tablets.
Zuckerberg, Facebook's controlling shareholder as well as its leader, is promising to put users' interests ahead of the company's financial interests.
"Simply put: We don't build services to make money; we make money to build better services," Zuckerberg wrote in a letter included in Wednesday's IPO filing. "These days, I think more and more people want to use services from companies that believe in something beyond simply maximizing profits."
AP Technology Writer Barbara Ortutay in New York contributed to this report.
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