The survey found that 61 percent of employers who use social networking sites are looking for information that supports their qualifications for the job; 50 percent are looking to see if the candidate has “a professional online persona;” 37 percent are researching what other people are posting about the candidates, and 24 percent are looking for a reason not to hire a candidate.

But employers are not just looking at Facebook posts, Twitter tweets and LinkedIn profiles -- 69 percent are researching anything that pops up about candidates on Google, Yahoo and Bing, compared to 59 percent last year.

Of those who decided not to hire a candidate based on their social media profiles, the reasons included:

• Candidate posted provocative or inappropriate photographs, videos or information: 39 percent did not hire such candidates

• Candidate posted information about them drinking or using drugs: 38 percent

• Candidate had discriminatory comments related to race, gender, religion: 32 percent

• Candidate bad-mouthed their previous company or fellow employee: 30 percent

• Candidate lied about qualifications: 27 percent

• Candidate had poor communication skills: 27 percent

• Candidate was linked to criminal behavior: 26 percent

• Candidate shared confidential information from previous employers: 23 percent

• Candidate's screen name was unprofessional: 22 percent

• Candidate lied about an absence: 17 percent

• Candidate posted too frequently: 17 percent

Moreover, people should continue to refrain from posting or tweeting negative comments after being hired, as more than half of employers (51 percent) use social media sites to research current employees, and 34 percent have found content online that caused them to reprimand or fire an employee.

“Just because you got the job doesn't mean you can disregard what you post online,” Haefner says.