Yes Regretting is possible for an online campaign. The best way to bring the visitors again if they did not complete the goal. You can re-target people through Google adwords and through Facebook FBX.
I assume that we are talking about specific situation where you already launched the campaign and didn't give the desired results.
So re-targeting will totally depend on the campaign type:
If we are talking about a Viral campaign, this will be amazingly hard, since the word of mouth and shares will go without a real control from your side, even if you have the videos or articles under you account control, you will not be able to stop people from copying, downloading and spreading it.
If we are talking about Online banners, then you are already committed to 1 month payment with the advertising website, so if it is a matter of banner and concept update it will be easy , usually you will be using a banners management system like OpenX or so to change your banner from your side, though some websites still uses a static method so you send them the updated banner and they change it, BUT if the issue is that your targeted segment is not using the advertising website, you still have to pay the one month fees, so you can think fast about different product or service to use for this website ads until the month ends.
If we are talking about a PPC campaign, then things will be easy, just update your ad settings.
and so on.
Yes It's easy to do that .. but , try to do 1 Ad and see the feed back before your campaign and also know what days are best & Time also ..
Best regardes
Online campaign are flexible, but it is more advised to do your research on your TA before actually launching your campaign. Do small tests on representative segments, measure and compare.
