Facebook, Amazon and Zynga will invest in a fund to help entrepreneurs develop applications and services for a new era of the social web.
The lion's share of the sFund's $250m (£160m) will come from venture capital firm Kleiner Perkins Caufield & Byers.
Details were announced at an event at Facebook's California headquarters.
"There's going to be an opportunity over the next five years or so to pick any industry and rethink it in a social way," said Facebook's Mark Zuckerberg.
"We think that every industry is going to be fundamentally re-thought and designed around people."
That was a view backed by KPCB partner John Doerr, best known for investing in Amazon, Google and Netscape.
"These social networks are going to go from a half a billion people to billions of people connected on the planet and so represents an extraordinarily exciting time on the internet," he told BBC News.
"Think of it as a quarter-billion-dollar party. The third great wave of the internet is mobile and social together. It's going to be tectonic," added Mr Doerr.
'Hopes and dreams'
The sFund will provide financing, advice and relationship capital for a new generation of start-ups to deliver on the promise of the social web.
Amazon will help businesses get access to the company's web services platform for one year, as well as provide business and technical support.
Facebook will contribute access to its platform teams, beta APIs, and new programmes like Facebook Credits.
The essence of the sFund is similar in concept to KPCB's $200m iFund aimed at companies that create applications for Apple's iPhone, iPod touch and iPad.
That fund, which started in 2008, has invested in 14 start-ups so far.
The sFund will be led by Bing Gordon, a partner at KPCB and former chief creative executive at Electronic Arts.
The main focus will be on social start-ups in all industries from consumer to enterprise and from health to mobile. It will not invest in direct competitors to Facebook, Amazon or social gaming company Zynga.
"We intend to be very loyal to the people we are working with. Our hopes and dreams get kind of enmeshed with theirs," Mr Gordon told the BBC.
"The companies we will invest in will be the Zynga of health, the Zynga of education, different kinds of commerce, of social utility, of finance. There is an opportunity to build Zynga-sized companies that will scale up.
"Social is just getting started and the opportunities are vast. As in the early days of the internet, the race is on."
For Google, which harbours social ambitions of its own, the creation of the sFund could be seen as a blow to the search giant.
"It is aligning everything against Google," said MG Siegler of the technology blog TechCrunch.
"I am sure the sFund will say they will be okay to fund things built on Google's upcoming social graph but it will be a long time before any of those companies pop up. This really does bolster the Facebook effect here."
Asked why Google is not taking part in this fund, Mr Doerr, who sits on their board, told reporters, "Google is still developing their social strategy. Stay tuned."
At the event the sFund's first investment was announced.
Cafebots closed a first round of $5m. The company is involved in what has been termed "friend relationship management". They did not make any comment because they are in stealth mode.
Other companies that KPCB said would have made the grade for the sFund were ones that the venture capital firm had invested in.
They included Jive, Lockerz and Flipboard.
"Everything is becoming more and more social," said Evan Doll, co-founder of Flipboard.
"This is about people. Applying that point of view to a lot of businesses and services will be great going forward and help the internet feel less like this cold and impersonal technological space," Mr Doll told BBC News.