Advertisers usually love to buy re-targeting impressions, but they can't find enough of them. Here are some tips for getting more.

Two years ago, my company received a request from an ad serving customer to re-launch its re-targeting and behavioral technology. Initially, I was skeptical about why any major online retailer would want re-targeting. Why would they pay to get their own site visitors back to their site? However, after doing some research, I realized it was a smart choice for any advertiser that monitored conversions. A user who has just visited, for example, an online retail site to check out prices for cameras is more likely to buy a camera than a random user who has never visited the site before. Therefore, showing an ad to this past visitor is much more effective than showing it to a random person. In fact, re-targeting usually gives 5 to 10 times performance lift over RON ads.

However, the low impressions available for re-targeting have been a major problem. Clearly, with more targeting, fewer impressions will be available. However, advertisers know how many users visit their site, and they see that they are only able to reach a small percentage of them again with the re-targeting buys they have in place. They often ask me where and how they can find more of their site visitors.

This is what I recommend to get more re-targeting impressions.

1. Buy impressions from the new internet
The new internet, or Web 2.0, is about games sites, social networks, video sites and social applications. I understand that advertisers may not love video sites or social networks -- they have shown poor performance in the past and people worry about their content. But millions of your site visitors are probably on these sites, and so they are great places to find and re-target them.

In addition, these sites rarely have much questionable content anymore -- a  particular concern for some companies that are new to the Web 2.0 world. These sites now use sophisticated technology to filter objectionable content and are clean. Also, don't worry about the low performance in the past. Re-targeting will find only the users on the site that are interested in your product. Performance of re-targeting is usually decent for the price.

2. Buying on poker sites
There are lot of "play" Poker sites with solid U.S. inventory. They are legal and fun, and they feature millions of users just playing cards, just like in Vegas. And many of those users may have visited your site. Also, with re-targeting, you are messaging only your existing customers and prospects who visited your site -- not to the online poker playing audience in general.

3. Buying on adult sites
I wouldn't recommend this for most advertisers, but if you are a direct marketer and are not sensitive about where your brand appears, the fact is that there are likely to be lots of your site's visitors who also visit adult sites. You can re-target them here if you want to.

4. Buy from more ad networks
Different networks reach different users. The more networks you buy from, the more likely you are to find more site visitors and get more re-targeting impressions.

In addition, the very best impressions on Web 2.0 sites are the first impressions that each user sees that day, and ad networks that sell the first impressions get a much higher performance than ad networks/exchanges that sell the later impressions that a user sees on the site.

5. Expand your frequency cap options
Many advertisers ask for a frequency cap of 1 (i.e., one impression per user per day on each site). These impressions are very effective and the ROI is good too. Yet, data has shown that the second and third impressions are often almost as good. So, expand your frequency cap. If the user has seen one of your ads on one site and then a few hours later sees another, he may still click on the second impression. The second and third (or fifth and sixth) impressions can often be effective and provide a decent ROI.

6. Drop that geo-targeting
Adding geo-targeting to a re-targeting campaign will usually not help you. Consider this: if you are a national online retailer and your re-targeting campaign is targeted to NY and California (where you sell most), you will still be losing out on many users from other areas (e.g., Chicago) who have visited your site before.

7. Extend your time window
Many advertisers choose to target their recent visitors only. Again, this may not be necessary and may be losing you some good re-targeting impressions. Users who have bought from you before are likely come back and buy more. It doesn't matter if they haven't been to your site for the past three or six months. Pitch them a great offer and they will come back.

8. Buy behavioral targeting, not just re-targeting
Re-targeting is a specific form of behavioral targeting. Behavioral targeting works on the principle that a human's past behavior gives you insight into his/her future behavior. If a user has visited your online retail site, he/she has shown an interest in buying your products. Similarly if a user has been visiting camera review sites, he/she is probably interested in buying a camera. This sort of behavioral targeting doesn't perform quite as well as re-targeting (as the user may be super loyal to another brand for example) but it performs well and it gets you more similar impressions.

In conclusion, re-targeting is a technology and a media buying strategy of increasing importance. With most internet users now on Web 2.0 sites, advertisers need a good way to find their audience there. Re-targeting is a proven way to do it. Used well it can be the best kind of advertising you can get for ecommerce, automotive, travel, lead generation and many other verticals.

Roy de Souza is CEO and co-founder of Zedo Inc.