Weiner, who had served as interim president of the professional networking site since January, also was appointed to LinkedIn’s board of directors.

Weiner is taking the helm of one of the pioneers in the social networking field, which is blossoming partly because people are pushing to improve their employment prospects amid the recession.

LinkedIn founder Reid Hoffman, who served as CEO from December of last year until this month, has become executive chairman of the Mountain View, California-based firm.

“LinkedIn was founded to harness the power of the Internet to create a tool that would help individuals become more effective and successful professionals,” Hoffman said in a statement. “Over the past six months, Jeff has done an exceptional job leading the company and I look forward to continuing the work that we have begun together.”

Founded in 2003, LinkedIn allows people to create profiles of themselves, connect with others and communicate with people in their extended networks.

While some other early social and business networking sites such as ZeroDegrees have faded, LinkedIn has grown stronger over the years. It boasts more than 42 million members worldwide, up from 30 million members last October.

The firm has secured more than $100 million in funding from investors including Sequoia Capital, Greylock Partners and SAP Ventures.

LinkedIn says it turned a profit in 2008 and expects to be profitable again this year. A shift in online recruiting practices is goosing those results.

Organizations that once relied on general purpose job boards are turning to alternative strategies, including social networking sites, search engine marketing and niche job sites.

In a May study by research firm AIM Group, nearly 45 percent of recruiters surveyed said they used networking sites such as LinkedIn and Facebook with mixed or great results.

LinkedIn offers services to recruiters including expanded results when searching the LinkedIn network, targeted job postings and direct access to candidates.

In February, LinkedIn said it saw responses to job postings on the professional network double from six months earlier.

Earlier this year, the company also introduced what it called “custom company profiles” with “viewer-aware” information. These profiles are designed to adapt to viewer characteristics such as location and industry.

Recruiting industry analyst Peter Weddle named LinkedIn one of the top 100 job boards this year. He says the site makes networking easier, but notes that networking is a time-consuming method for landing candidates.

LinkedIn “is a site with great potential for recruiters,” Weddle says. “We’re still trying to figure out how to use it efficiently.”

Weiner has more than 14 years of consumer Web experience. Before joining LinkedIn as interim president, Weiner was executive in residence at venture capital firms Accel Partners and Greylock Partners. Greylock helped finance LinkedIn.

He also held leadership roles at Yahoo, most recently serving as executive vice president of Yahoo’s network division with responsibility for Yahoo’s consumer Web product portfolio, including Yahoo’s front page, mail, search and media products.