While social games are booming online, the killer app of the genre, or "the Mario of Facebook" is still to be designed according to the site's platform manager Gareth Davis.
He opened GDC with a keynote talk about the social games revolution, running through why Facebook games have become such big hits.
Davis said that social games and apps on Facebook have sparked a profound shift in games design.

"Facebook is at the centre of a people powered social web." It's hard not to disagree. The site has 400m users a month, 200m a day logon for sessions lasting around 55 minutes each.
In tandem with this there are a million devs making Facebook Platform Apps and using Facebook Connect.
Games are one of the most popular parts of the social networking service with 200m playing games on Facebook each month.
"We have a mass audience," said Davis. "We have moved beyond the core consumer and have people playing games across every demographic."
But, said Davis, despite their being some high profile successes in social games, "the iconic Facebook game still lies ahead of us".
"The Mario of Facebook is out there and will likely come from someone [at GDC] - it's likely your next game, which is very exciting. We think this game will change everything - and we're looking forward to playing it."