There are plenty of unadvertised or "hidden" jobs out there, but discovering them takes a little bit of luck and a lot of smart discovery tactics.  
Fred Coon, an author, licensed employment agent, and CEO ofStewart, Cooper & Coon, says experts estimate that between 80% and 85% of all jobs openings are unlisted. 
"Current social media trends and technology advances allow companies to find applicants without listing a position," Coon says. "Some companies don't like to advertise on job boards because of the cost. And the ones that are free aren't a great option, either."
Employers are finding that when they list an opening on a free job board, the number of unqualified applicants that reply overwhelms them, and they wind up spending untold hours and resources trying to screen each candidate. "Therefore, it is much easier for them to look on social media platforms for good candidates for their open position. They can screen applicants on LinkedIn and Google+ and other platforms without excessive costs," Coon explains.
If you're able to find these hidden jobs, you could be doing yourself huge favor. 
"Finding those hidden job postings first affords you a fighting chance because you get there before anyone else does," Coon says. "If this happens, you greatly improve your visibility and the opportunity of being considered for the position increases."
Here are eight tactics for successfully penetrating the "hidden job market."
1. Join industry-related groups. Join associations, Chambers of Commerce, meet-up groups, Toastmasters, etc., and start building contacts before you need them, Coon says. "Consider volunteering to give a talk at a meeting of one of these entities, as this is a great way to get noticed."
2. Establish yourself as a source of information in your industry. Send each of your individual contacts within your network links to articles of interest once or twice a year, Coon suggests. "When you send these links, keep your email short: 'Saw this and thought you might be interested…' This way, your name becomes associated with good information and you are seen as a valuable, well-read resource."
3. Talk to insiders. "Try to talk with executives in various companies and industries to learn what is happening in their spaces so you know where to align your career path as well as your job-search efforts," he says. "Your next great opportunity may be in a space you never thought possible, but you'll never know if you don't explore."
4. Pay attention to the news. Stay on top of any local business journals and TV news for information on what's happening with companies in your area. "If you hear someone interviewed on news-radio, send them a note that you appreciated what they had to say and would like to get together over coffee to learn more," Coon says.
5. Search company "Careers" pages. "Research and target companies you are interested in — most companies will post on their own website and never go to outside job boards or recruiters." In fact, many companies have internal referral programs in place, so existing employees make referrals and thereby eliminate the need for the company to conduct a formal search.
6. Build and maintain relationships with recruiters. "The best way to do this is to update your resume every few months so you can send the latest version to them," Coon says.
7. Use LinkedIn wisely. Keep your profile up-to-date, and refresh it regularly. "Join groups and participate in discussions so people become familiar with your name and may seek you out," he says. "Remember, recruiters and companies often purchase memberships that give them a 'back door' to see who is active in their field and what they are saying, so be certain to keep your discussions positive and constructive."
8. Target carefully. Pick the companies where you would like to work; do your homework on why you want to work there; and identify those things that you can relate to and like about the company, Coon says.
Then, do your research to identify the decision makers, or people high up enough in the company to know the decision makers, and connect with them on LinkedIn. "Send them something of value: an article or anything that would help them, not you," he says. "And don't ask them for anything in your first few communications."
Eventually, Coon says, they will be receptive if you have been helpful — and you'll be the first person they think of when a job becomes available. 
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