More companies are trying to tap Facebook Inc.’s 750-million-plus user base to find new employees, threatening traditional job boards and competing with LinkedIn Corp., which has dominated the online professional networking arena.

Facebook’s use as a job-recruitment tool remains small, but its appeal may be growing. Some recruiters say they have all but eliminated their spending on job boards, which can charge a few hundred dollars per job posting, depending on volume. Others note that while LinkedIn contains a more comprehensive résumé database, candidates tend to value referrals from their connections on Facebook more.

The majority of social-media traffic to Waste Management Inc.’s careers website comes from Facebook, beating out LinkedIn, said Jenny DeVaughn, manager of social media and employment branding. The Houston-based environmental services company is currently trying to fill 1,500 positions—from software developers to garbage truck drivers.

In addition to posting jobs and videos of current employees on its Facebook page, the company has recruiters and other employees find user groups and join discussions.

When asked for comment, LinkedIn referred to its chief executive’s remarks from last week’s conference call to discuss earnings. During the call , CEO Jeff Weiner said users tell the company they want to keep their personal and professional networks separate.

Indeed, Jeff Vijungco, vice president of world-wide talent acquisition for Adobe Systems Inc., said that in focus groups, prospective job candidates were sharply averse to being contacted through Facebook for jobs.

“The antibodies kicked in pretty quickly. They thought it was very invasive,” he said. The company posts job openings on its Facebook page, but Mr. Vijungco said they have had more success finding employees through LinkedIn.

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