Let's start this article with a brainteaser: What attracts 174 million eyeballs every month and is often free for advertisers? The answer: Craigslist, the new king of the classifieds. Are you on it? If not, why not?

There's really no good excuse. These days, having your listings online isn't just an option -- it's a requirement. NAR reported last year that 87 percent of residential home buyers start their real estate searches on the Internet. If having your listings online isn't a requirement, I don't know what is.

I visited Craigslist the other day and found many listings from Realtors and real estate companies. I saw an ad from a Realtor in New Jersey who specializes in short sales (clearly a hot market these days). And I learned other Realtors are using Craigslist to drive traffic to their websites -- a grand idea. (I read about one Realtor in particular who said he gets between 50 and 100 visits each month to his website that come directly from Craigslist.)

I also found an ad from a Realtor looking for an office. It read: "Excellent Realtor - Experienced, Reliable, Trusted."

Even the large real estate companies are tapping Craigslist to recruit new blood. I found an ad recently from Coldwell Banker, obviously a well-established real estate brand, that said it was "seeking licensed Realtors who are highly motivated" to join its operations.

All this online real estate activity doesn't surprise me in the least. Why? Because the numbers behind Craigslist are staggering: nearly 87 million users and 35 million ads posted monthly. In my opinion, it's yet another proven digital mouthpiece to get the word out about your listings.

And its popularity is growing, particularly strong in the Midwest and South where its growth has hit the stratosphere -- in some cases 1,000 percent year-to-year. And if you're looking to attract international clients, Craigslist launched 120 new cities this past spring, most of which were outside the U.S. And future sites will largely be outside the United States and Canada.

So as newspaper execs watch their classified ad revenue dwindle, Craigslist reported earlier this year its housing ads were up 85 percent year-to-year, with rental ads up 120 percent and real estate up 70 percent.

Now before you call or e-mail about this last sentence, hold on a minute. I'm not suggesting you drop newspapers from your advertising arsenal. I'm just pointing out an observation. If you're having success in print, by all means continue.

With that said, here's another Craigslist plus: it's free and easy for consumers to use. They can search for free, and perhaps more importantly to you, they're free to contact you -- the Realtor, if you're on it and point them to your phone number or website.

But for all the good things Craigslist offers, it's not perfect. Scams happen. One you may have heard about involves a Realtor who posted a listing for rent on Craigslist. Then a scammer created a new ad using that Realtor's ad and listed rent at substantial discount. A consumer responded to scammer's ad and was directed to a website where she was asked for her social security number. Be sure to tell consumers to verify they're working with a real estate licensee by calling the local association or office where the Realtor works.

To its credit, Craigslist is implementing tools to prevent future scams and inappropriate content.