The section features dedicated pages for athletes and sports, including a complete timeline history of the competition since the 1800s.
The IOC said the portal would create a “social media stadium”.
However, restrictions on what athletes can or cannot post will restrict some content from being published.
Participants are subject to tight guidelines over content posted on Facebook and Twitter, particularly in relation to brands and broadcasting deals.
It restricts the posting of any video from within an Olympic venue.
Mark Adams, from the International Olympic Committee (IOC), said that while visitors to the Games would be able to post videos and stills, athletes’ activities would be curbed.
“It depends on where they are,” he said.
“If they’re in a stadium, they can’t. We have a relationship with various broadcasters around the world which provides the funding [for the Games].”
In addition, he said, the IOC would be watching for any attempted “ambush” marketing.
“It’s something we always have to keep in our mind,” he said.
“It does take away money from the Olympic movement. It’s something that we have to protect.”
Facebook, which announced the portal at its central London offices, said it hoped the portal would mean Olympics fans could interact with athletes in a way that had not been possible in previous Games.
Alex Balfour, from the London Organising Committee of the Olympic Games (Locog) said there was now a “perfect storm” of technology to allow a “really rich experience” wherever fans were in the world.
“We want make sure our Games is available to that new audience of digital consumers,” he added.
Facebook said it would allow fans to use the network to discover footage of their favourite athletes – but some content would be geo-targeted, meaning certain footage might not be available in certain regions of the world.
Mr Adams admitted that the IOC had been slow to adopt social networking, but was now ready to embrace it for London 2012.
“The way I like to think about the IOC and our relationship with social media is that the Olympics is one of the oldest social networks that has ever been.
“Everyone has an experience and shares that experience with their friends and their family – everyone has an emotional attachment to the Games. We’re just digitising that experience.”
Former world tennis number one and Olympic gold medallist Boris Becker told the BBC that using social media could help athletes prepare.
“It’s very positive. It gives athletes the chance to get real opinions and real questions and to answer back.
“It’s fun – everyone’s online anyway. It’s impossible to think all day and all night about the next match, interacting with fans is a good thing.”
However, he warned that it was inevitable that some athletes might not think before they tweeted and so land themselves in hot water during the Games.
“The world and people are not perfect,” he said.
“There will always be athletes who will take it out of line, but that doesn’t mean that the platform is wrong.”