Popularity of online commmunities such as Myspace is growing
LinkedIn, a networking site for professionals, has raised $53m (£27m) of new funding from investors.
The financing by venture capitalists values the Silicon Valley start-up at more than $1bn, reflecting investor confidence in online communities.
Bain Capital Ventures led the site's latest round of funding, giving investors a 5% stake in the firm.
Existing partners Sequoia Capital, Bessemer Venture Partners and Greylock Partners also invested in the site.
The company has so far raised a total of $80m in funding after the latest round of money-raising, the site's fourth so far.
The company, which is profitable, makes money from advertising and premium subscriptions.
LinkedIn's European chief executive Kevin Eyres said the firm's business model was different to that of many start-ups of the dotcom boom of the late 1990s.
"Back in the bubble, people only had advertising based around online ads. We have three other business models," he said.
23 million members
Five-year-old LinkedIn has 23 million members worldwide and attracts 1.2 million new members every month, according to the the company.
LinkedIn connects people in the workplace, helping them search for new jobs and make professional contacts, whereas people use sites such as Facebook, MySpace and Bebo for social reasons.
Networking sites have been on the rise since Microsoft paid $240m for a 1.6% stake in Facebook last year. That deal valued Facebook at $15bn.
LinkedIn plans to use the new funds to add features to its site and expand its service in other languages.