Silicon Valley star Sean Parker said Monday that Facebook would have to blunder in a big way for Google's social network to steal its crown.

"Facebook would have to screw up royally and Google would have to do something really smart," Parker said during an on-stage interview that opened a Web 2.0 Summit in San Francisco.

Parker co-founded controversial music-sharing service Napster in the 1990s and his role in Facebook's rise was woven into the hit Hollywood film "The Social Network."

"It is tough to compete with network effects," Parker said when asked his thoughts on the threat posed to Facebook by Google+.

Google needs to get Facebook users to switch allegiances, then do the same with those people's online friends, and those people's friends, and so on, explained Parker, who owns part of Facebook.

A threat to Facebook is "power users" behind attention-grabbing content turning to rival online venues to escape drowning in the flood of posts, according Parker.

"I don't think privacy is Facebook's biggest problem," Parker said, touching on a topic for which Facebook has been criticized.

"The biggest problem is the glut of information that power users are overwhelmed with," he continued. "Maybe the threat to Facebook is the power users have gone to Twitter or Google+."

He supported Facebook improving ways for its approximately 800 million users to more selectively share posts, pictures or other information with one another.

"Sean is really one of the great prophets of our industry," said Saleforce.com founder Marc Benioff, whose online business software startup has blossomed into a multi-billion-dollar poster child for cloud computing.

"Facebook, in many ways, is eating the Web," he continued during a talk at Web 2.0. "Facebook is becoming a vision of what the next-generation consumer operating system is."

Online auction powerhouse eBay and its thriving financial transactions service PayPal also see strong "network effects" providing defense from Google's growing commerce platform.

"I agree with Sean, network effects are powerful things," eBay chief executive John Donahoe said during an on-stage interview at Web 2.0.

Google has a tremendous online search and advertising platform and Facebook a widely embraced social platform, while eBay has an entrenched "e-commerce" platform, according to Donahoe.

"The wall between e-commerce and retail is crumbling amazingly fast," Donahoe said. "The large retailers are banging down our doors and saying 'The world is changing; we need help'."

EBay last week launched PayPal Access online identity program and an open X.commerce platform for payments to let merchants large or small tap into Internet age cashless transactions.

X.commerce is intended to match merchants with independent developers building innovative ways to handle check-outs at websites, inventories, calculating taxes and other aspects of running shops with online outlets.

Meanwhile, PayPal Access will let people shop at websites anywhere on the Internet using names and passwords from accounts at eBay's widely used financial transactions service.

EBay boasted that there are more than 100 million PayPal accounts in 190 markets worldwide.

Google said last week that its online social networking challenge to Facebook is growing fast and has topped 40 million users.

"People are flocking to Google+ at an incredible rate and we are just getting started," Google co-founder and chief executive Larry Page said during an earnings conference call.

Page said Google+ style social features will be "baked in" to the Internet star's other offerings.

The Internet giant on September 20 opened google.com/+ to the public as it ramped up its challenge to Facebook.

Google has also been beefing up its e-commerce platform and letting people use some Android smartphones to find local bargains and pay by tapping handsets on sensor pads at checkout counters.