Listen Up! If you're not advertising on internet radio, you could be missing out.

According to a 2004 study by media research firms Arbitron Inc.and Edison Media Research, internet radio has an estimated weeklyaudience of nearly 19 million Americans and growing. Not only arepeople listening in online, they're also buying online.

Monthly internet broadcast (radio and video) users mightrepresent only 26 percent of the online audience, but theyaccounted for an estimated 42 percent of online spending.Advertisers can reach an audience that's in listening andshopping mode.

Thinking of advertising on internet radio? Here are a few tipsbased on audience demographics and behaviors:

• Test a newoffer. About 28 percent of internet broadcast users arelikely to try a new product or service vs. 17 percent ofnonbroadcast users. So launching a new product through internetradio could give your initial sales a boost. You'll also likelyreceive immediate customer feedback or testimonials to help youfurther refine your product or service and marketing pitch.

• Appeal to a"hip" audience. Although the age range ofbroadcast users is 12 to 54 years old, the highest concentration ofusers falls into the 12- to 34-year-old group. They are atechnologically savvy group in tune with DVDs, cell phones,messaging, video games and other media products. Communicationgadgets will sell well to this crowd. Yet, even if you aren'tpromoting these types of devices, tailor your advertisement'smessage to address the concerns, needs and wants of a sophisticatedyoung audience.

• Use a URL in yourad. Forty-two percent of the internet radio audience haslistened in while shopping or researching a product or serviceonline, so invite them to your website. To sweeten the offer andtrack your radio advertising results, promote a particular page onyour site, such as www.company.com/radio- just don't make it toolong, or people can't remember it. You can use web analytics totrack page traffic and also embed code in the links on this page totrack leads and sales from it as well.

Wondering where to start with internet radio? According toAccuStream iMedia Research, the top five internet radio sites inMay 2004 were: Shoutcast, Net Radio Sales Network, AOL RadioNetwork, LaunchCast powered by Yahoo! and Chaincast/StreamAudio.

AccuStream iMedia Research, which provides data and analysis onstreaming media and on-demand broadcasting, noted that while AOLusers already pay a monthly subscription fee and can thereforeaccess the network's radio programs, a majority of internetradio stations are free. This was a major factor in the solidgrowth of the listening audience across the major players fromMarch to May 2004, and a growing consumer audience is a compellingreason for advertisers to investigate their opportunities.

Before you launch an internet radio ad campaign, however, tunein and experience it. You'll get acquainted with the newbroadcast world of your future customers.

Speaker and freelance writer CatherineSeda owns an internet marketing agency and is author of SearchEngine Advertising.