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As the downturn continues, millions of corporate managers—gripped by the job jitters—are rushing to join online social networks in a scramble to build their social capital. The popularity of sites such as LinkedIn is soaring: less than a year ago the site had little brand profile and was seen mostly as a venue for corporate suits trolling for professional contacts while plotting their next career move. Facebook, by contrast, has largely attracted individuals seeking a compelling site for fun social networking.

Today LinkedIn’s year-on-year growth is up nearly 200 percent in the United States and it now has more than 35 million members—many of whom were formerly employed within the hard-hit financial sector. And it’s just one of the many sites to which recession-struck managers are flocking: Xing (based in Germany), with its 7 million members and special Lehman Brothers alumni section, and Meet the Boss (based in the United Kingdom), which restricts membership to C-level financial types, are also experiencing burgeoning membership levels.

This surging popularity of online...