They may be called social networking sites, but Twitter, LinkedIn and Facebook could just as easily be named "first impression" job sites because that's where recruiters and hiring managers are more likely than ever before to get their first glimpse of you as a potential job candidate.

A survey of 600 human resources professionals and recruiters by the recruiting software company, Jobvite, found that 83% of them plan to use social networks to hire this year.

Job search experts will tell you that the best networking site today is LinkedIn. I can pretty much attest to that. When my colleague at Merrill Lynch got a job at UBS, I sent him a message through LinkedIn and dropped the hint, that if he ever needed any help to keep me in mind.

A couple of weeks later, he called after connecting to another colleague of ours via LinkedIn, my former boss at Merrill, who he asked what I was like to work with. He must have liked what my boss said because he hired me on the spot, without having to go through a gauntlet of interviews or jump through all those human resources hoops.

Here I was with a new job that paid me more than I ever made before without having to submit a resume, or references, or taking any personality tests.  And it happened because I was on LinkedIn.

Kevin Donlin, co-director of Guerrilla Job Search International, is quoted in U.S. News and World Report as saying, "If you're not on LinkedIn, you do not exist to recruiters." Donlin also says to make sure your bio is up to date and complete and that you have a professional-looking photo. He adds that once a comment or photo goes online, anyone might see it so don't complain about your job on Facebook or tweet when you've been drinking.

Think of these sites as where you'll be making your first impression to someone who has the power to hire you. If you're looking for a job, reach out to your contacts as well as those "special interest” groups and alumni chapters you can join on Facebook or LinkedIn. Both offer simple access to people working in your field or at companies you might like to join.

Twellow.com is the Yellow Pages for Twitter. You can search for potential networking contacts by writing job titles such as "communications manager" or "financial writer" in Los Angeles. What will come up is a list of people ranked with the most followers. Send them a tweet.

You can also connect with like-minded people by joining group chats and build relationships with potential contacts by sending them an article you think they'd be interested in. Re-tweeting is both an ego booster for the person you've re-tweeted as well as a way to connect. Another way is to simply replying to someone's tweet.

That's a recommendation from Jason Alba, CEO of job coaching website JibberJobber.com. He told U.S. News "that way you'll avoid looking desperate while you get on the radar of someone who can help you."

The trick I've learned with Twitter is that the more you help others, the more likely people are to help you. Twitter is no place for a hard sell. Give helpful information and you'll be loved. Tout yourself and you'll be loathed.

As for social networking sites, the rule is to keep it light and "social.”  When you connect to someone invite them for coffee or to chat by phone as a way of learning about them and their companies. Whatever you do, do not ask them for a job.

As an article in U.S. News Report on how to use social networking sites put it, "Make a friend before you make a sale."