Facebook hitting 500 million members this month, as rumors swirl that Google is readying its own social networking venture, shows how the tech world’s center of gravity is changing.

“Social optimization” is spawning a burst of startups and ancillary services aiming to help companies make money off burgeoning social media web traffic. It’s similar to the universe of companies providing web analytics and search optimization services that emerged over the last decade around the search industry defined by Google.

Gigya Inc. of Palo Alto, California, for example, shifted its business model late last year to connect other websites to as many as 50 social networks in an effort to increase traffic, promote content discovery, target advertising and track results.

Gigya had a different focus previously that wasn’t making enough money, and by the second half of 2009 it became clear that publishers like Huffington Post and USA Today were getting more traffic from social referrals than from search engines, said CEO Dave Yovanno.

So Gigya became a “social optimization” company, and now it charges companies $1,700 a month for its web-based services. Customers include ABC, ESPN, Reuters, Time, Turner, Answers.com, OpenTable and Intuit.

“It became obvious to us that there is an addressable market of at least tens of thousands of online businesses who are willing to pay at least tens of thousands of dollars for both the technology and service for social optimization, in the same way they have paid for search optimization,” Yovanno said.

“We’re helping businesses realize that if you optimize for it in the right way, social could actually be your No. 1 source of traffic,” he said.

The 50-person company recently hired a half-dozen people in its headquarters, where 20 people work. It expects to hire as many as 20 more over the next year, particularly in sales, business development and client services. Revenue is under $5 million, but the company expects to be cash flow positive next year.

Talk is widespread that Faceboook and “social search” represent a potential threat to Google, which has prospered primarily by answering keyword-based queries, and the search giant is widely expected to mount a social response.

Yovanno says he expects social marketing will actually complement search, but Google and other big web properties, like Yahoo and MSN, are not likely to sit idly by while a new market explodes.

In fact, Google CEO Eric Schmidt’s venture fund, Innovation Endeavors, put seed money last year into Palo Alto, California-based VideoGenie, a startup that in March launched a service that lets companies gather video testimonials from customers for use on websites and posting to social networks, among other places.

VideoGenie CEO and founder Justin Nassiri says his company makes it possible for consumers can go to a website for the first time and be greeted by a video of a friend talking about a brand.

Like Gigya, VideoGenie is agnostic about where the video gets posted.

“We’re not part of the war between Facebook and Google. We sit in between,” Nassiri said.

Compass Labs, which launched in San Jose in May, similarly says that it can target advertising to people in real time based on the content of online comments on multiple social networks. The company this month raised $5 million with investors including NEA, Triple Point Capital and Netscape co-founder Jim Clark.

Mike Grehan, a vice president with Incisive Media and producer of the Search Engine Strategies conferences, said that social media has become “a major new planet in the search solar system.”

As a result, September’s Connected Marketing Week conference in San Francisco is for the first time featuring more than a half-dozen workshops focusing on the expansion of search to social media. That will include forums specific to real-time communication and blogging, and a social media overview.

One tool for socializing websites is identity authentication, which websites increasingly allow users to accomplish with the click of an icon using account information from one of their social networks.

Like competitors, which include services like ShareThis, Gigya is neutral about which social network people use and it provides clients easy access to many networks through a single door, as well as analytics on traffic that the social networks themselves often do not make available.

Gigya is working with Adobe’s Omniture to build social data into reporting products. Adobe is a Gigya investor, along with Benchmark Capital, Mayfield Fund and DAG Ventures.

According to a recent Gigya report, those who use a social service to sign in at a third-party site use their Facebook identity 46 percent of the time. Google was second at 17 percent, Twitter third at 14 percent.

Streamlining sign-ins makes it easier for users to share information to their social networks ranging from editorial content to photographs of merchandise with pricing and links.

Launched to the public in 2007, ShareThis is a 20-person company that has raised $21 million, the last round led by Draper Fisher Jurvetson, and uber-venture capitalist Tim Draper is on the board of directors.

ShareThis CEO Tim Schigel believes social marketing will drive an increase in display advertising because it offers a new way to segment audiences.

“With search, you’re only able to get to people when they’re searching,” he said.

Seth Greenberg, director of national media and digital marketing for Intuit, said that just since launching with Gigya in December, 100,000 customers have sent comments about TurboTax to the news feeds of an estimated 15 million friends.

The amount of traffic the company is getting from social network clickthroughs is now more than 20 percent of links from other sites and could top 40 percent by next year, and social network clickthroughs lead to more new business than search clickthroughs, he said.

“That is phenomenal when you talk about the horse race between social networks and traditional search engines,” he said.

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Patrick Hoge writes for the San Francisco Business Times.