Riju Parakh wasn’t even looking for a new job.

But when a friend at Ernst & Young recommended her, Ms. Parakh’s résumé was quickly separated from the thousands the firm receives every week because she was referred by a current employee, and within three weeks she was hired. “You know how long this usually takes,” she said. “It was miraculous.”

While whom you know has always counted in hiring, Ms. Parakh’s experience underscores a fundamental shift in the job market. Big companies like Ernst & Young are increasingly using their own workers to find new hires, saving time and money but lengthening the odds for job seekers without connections, especially among the long-term unemployed.

The trend, experts say, has been amplified since the end of the recession by a tight job market and by employee networks on LinkedIn and Facebook, which can help employers find candidates more quickly and bypass reams of applications from job search sites like Monster.com.

Some, like Ernst & Young, the accounting firm, have set ambitious internal goals to increase the proportion of hirings that come from internal referrals. As a result, employee recommendations now account for 45 percent of nonentry-level placements at the firm, up from 28 percent in 2010.