SAN JOSE, Calif. — It may be too soon to equate the Xooglers, as members of the ever-expanding network of ex-Google employees call themselves, with the “PayPal Mafia” — the founders and early employees of the online payment company who went on to start Yelp, YouTube and LinkedIn.

But perhaps not for much longer.

Former Googlers, many of them flush with the proceeds of Google’s successful IPO in 2004, have long left the Internet giant to become investors or start their own companies. But now, for the first time, say people familiar with the growing network, there are Xooglers at every level of the Silicon Valley startup hierarchy.

Within that network are angel investors, partners at venture capital firms, entrepreneur mentorship organizations and Google Ventures, a full-service venture capital operation that offers a unique set of resources, including the ability to tap into Google’s engineer recruiting network.

“The Google network is far and away going to be the most powerful network and ecosystem. There is an ex-Googler now at pretty much every top-tier (venture capital) firm, so if you’re an Xoogler with a startup, you can instantly get yourself a meeting at Greylock, at Sequoia, at Kleiner Perkins, at Andreessen Horowitz, at Khosla,” said former Googler David Friedberg, CEO of WeatherBill, a 4-year-old San Francisco startup that recently announced $42 million in backing from Khosla Ventures and Google Ventures.

Like Friedberg, many Xoogler entrepreneurs, after toiling at the Mountain View Internet giant, tend to think big.

Among those are Dan Siroker, who after quitting Google in 2008 to serve as one of presidential candidate Barack Obama’s secret tech weapons, is now CEO of Optimizely, a San Francisco startup. Siroker founded the company last year with fellow ex-Googler Pete Koomen, and the company’s software has been used to do everything from boosting fundraising for the Haiti earthquake to helping the Democratic National Committee’s Facebook applications go viral.

“I just really like to build things,” Siroker said. “Going to Google, I really wanted to learn the skills that would make me a successful entrepreneur on my own.”

WeatherBill, whose chief technical officer Siraj Khaliq also came from Google, aims to build a highly profitable business that will also help the world’s farmers cope with climate change. The company uses huge data sets to predict weather patterns with enough accuracy to market weather insurance that helps farmers lock in a return on their crops.

The network of former Googlers has yet to spawn a company the size of Yelp or LinkedIn, although Twitter co-founders Biz Stone and Evan Williams had short stints at Google. Many Xoogler startups — staffed with small teams of a half-dozen or fewer engineers — are acquired by Google or another company. One example was Facebook’s recent purchase of Beluga, a three-person startup that offers group messaging apps for smartphones. But Friedberg believes a big Xoogler company is coming.

In its hiring process, and in an internal culture that tends to teach people that “anything is possible,” Google tends to create entrepreneurs who aren’t daunted by sweeping or complex challenges, Freidberg said.

“I think there is a selection process at Google for people who want to think big, who are challenged by big problems and want to solve big solutions,” he said.

Attending a recent TED conference in Long Beach, Calif., a thought conference that lures many Silicon Valley tech executives, Friedberg said it often felt like a kind of high school reunion for former Googlers.

“I know almost all the executives at Facebook, all of the management team at AOL — all of the vice presidents have some Google connection,” he said. “We all used to work together at Google.”

There’s a reason for that. Two of the most prominent former Googlers are Tim Armstrong and Sheryl Sandberg, respectively the CEO of AOL and the chief operating officer of Facebook. Others agree the network appears to be broadening and maturing. Last September, a group of seven ex-Googlers launched AngelPad, a San Francisco mentorship program intended to help Web technology startups.

“I’ve definitely noticed a rise in Xoogler entrepreneurial activity driven by the critical mass of Google alumnus across the startup ecosystem — from founders, to investors, and at potential acquirers,” said Hunter Walk, a YouTube executive who has also been an angel investor in an ex-Googler startup.

“There’s a continuum that starts with the entrepreneurs,” agrees Bill Maris, the managing partner of Google Ventures. “You can pick out any point along the chain and see people doing interesting things.”