After watching the rise of YouTube, Microsoft launched its own Soapbox video site. After seeing Craigslist pull in huge amounts of traffic, the Redmond company launched its own online classifieds, Windows Live Expo. Its Evite competitor? That would be Windows Live Events.

And now, with social networks grabbing the attention of the online world, Microsoft is doing something extraordinary: It’s not really competing at all.

Rather than launching a direct rival to Twitter, Facebook or LinkedIn, Microsoft is working with those services to incorporate their features into its own products. Analysts say the newfound pragmatism reflects the struggles of such services as Windows Live Expo, Windows Live Events and Soapbox — all of which have since been abandoned — and Microsoft's focus on challenging Google in the search market.

More broadly, it also reflects a growing sentiment in the tech industry that the big social networks have achieved a critical mass that makes them practically untouchable to potential competitors (though perhaps not to potential acquirers). That affects the strategies not just of Microsoft but also of Amazon.com and countless tech startups.

Tech financiers in 2010 should avoid giving money to “anyone trying to build his own social network,” said Glenn Kelman, the CEO of Seattle-based online real estate company Redfin, during a recent Washington Technology Industry Association panel. “I think you should use the existing networks that are out there.”

Startups that have followed that strategy include iLike, the Seattle-based music service recently acquired by MySpace. Its Facebook application is widely used to track and share information about music. RealNetworks integrated connected to Facebook and Twitter into the latest version of its RealPlayer software. And Amazon has been making more serious use of Twitter.

Under a program announced this month, Amazon is giving its legion of affiliates — who direct traffic to Amazon through web links and banner ads — a way to make money doing the same thing on Twitter. Affiliates collect referral fees if someone clicks on a link or ad and ends up buying something from Amazon. Now they can “tweet” about a product for sale on Amazon, and if the tweet results in a sale, they’ll get a fee.

“There’s a substantial amount of traffic that’s being generated off Twitter for Amazon,” said Brian Walker, a Seattle-based e-commerce analyst for Forrester Research, a technology research firm. “Now they’re adding to the ability to capitalize on that and promote it as an affiliate.”

The new program represents an evolution of Amazon’s relationship with Twitter. Jeff Bezos, Amazon’s founder and CEO, was an early-stage investor in the microblogging site, and Amazon has used Twitter to send out deal alerts and draw attention to new services. Now Amazon is seeing possibilities in Twitter as a sales referral engine.

Microsoft offers some social networking features as part of its Windows Live service, but it has been working openly with all three of the major outside services — Twitter, Facebook and LinkedIn — rather than competing directly against them.

The new Outlook Social Connector will bring feeds from LinkedIn and other services into Microsoft's widely used email client.

The company on Nov. 18 announced plans for a new feature in Outlook that will let social networking sites incorporate features from their services into the widely used email program. Business-oriented social network LinkedIn said it would be the first outside service to take advantage of the feature, letting people follow and send messages to their LinkedIn contacts through the Outlook interface.

A new overhaul of Microsoft’s MSN.com portal will let users incorporate their personalized Facebook and Twitter feeds into the MSN home page. In October, Microsoft reached deals to incorporate data from Facebook and Twitter into results from its Bing search engine. Microsoft also has a minority ownership stake in Facebook and an advertising partnership with the site.

Although the company gives up a measure of control — and potentially profits — by not operating a direct Twitter or Facebook rival of its own, it also can leverage the momentum and credibility of those services by working with them rather than against them.

“I think they’ve looked at their online business pretty carefully and realized that there was no value in going after every single thing that a competitor had,” said Matt Rosoff, analyst at the Kirkland-based Directions on Microsoft research firm.

Instead, he said, the company is putting most of its focus on making its Bing search engine a credible rival to Google. That effort includes Microsoft’s pending search advertising partnership with Yahoo, its longtime rival.

Still, tech companies’ new interest in the big social networks has increased speculation that the social networks could be “meaningful acquisition targets,” said Walker of Forrester Research. He noted, however, that such sites have proven difficult to monetize and the “jury is still out” on their business models.