What audience size do you need for a successful retargeting campaign?

[ProjectLabs]

I recently launched a trial of a retargeting campaign but after a month I have only 100 impressions and 0 clickthroughs.

I am working in a competitive space but I placed a relatively low bid because I read that retargeting campaign banner ads should cost less. The number of people who have been added to the retargeting list by visiting the site is under 10,000.

What do you think is most likely to be the problem causing a low number of impressions and clickthroughs? Can a retargeting campaign be successful with a small audience size?

[JasmineA]

John and Rui have handled the technical aspects of how retargeting is really valuable, but with the number of visitors you have in the retargeting list I'm really curious what other settings you have for this campaign.

How many impressions have been set per unique visitor? 
How low are your bids? I would say keep them at about $1.50 CPC (not CPM) and see how things go. If you're already at this level then you may want to consider increasing your costs a little more.

Yes Retargeting is going to be cheap, but please keep in mind that Click to Conversion is not the only way to track retargeting progress. Be sure to use the View-Through Conversion column as well.

CTRs will always be low because that is the nature of the display network (sometimes getting a .12% CTR is as good as it gets).

Other things you need to pay attention to are how old is your messaging? What is the message you are using for everyone? Do you only have one product and so is one message OK? As John mentioned in his comment - you should have multiple segmented lists from the initial retargeting list. Some people are not ready for a hard sell. Some need to be reminded that you exist first.

Also, what pages are you using for your retargeting code? This will also have a significant impact in how you see returns come in. (Hint: start with Confirmation or Thank You pages first, then slowly build out from there and segment the lists accordingly)

[RuiZhiDong]

Well 100 impressions is nothing. You need a lot more impressions to get some clicks. As John has suggested, try increasing your bids.

A retargeting campaign can certainly be successful with a compelling ad even if the small audience size is small

I have a client who wanted to say thank you to a list of 80 high value customers. So I cookied these customers and displayed thank you images as part of the remarketing campaign which got great feedback

[john4math]

Sure, 10,000 people is enough to run a retargeting campaign.

You might try bringing up the bid to get some more impressions and see how it goes.  100 impressions isn't enough to tell much of anything.  Retargeting does tend to have the highest ROI of any display advertising if you target it properly.  Since the users in your retargeting list are more likely to convert on your site since they've been there before, you can tolerate a higher CPC with retargeting as compared to other display campaigns.

Are you segmenting your retargeting lists into many smaller lists?  You can split your lists into users that have made it further down your conversion funnel, and bid higher the further they've made it down the funnel already (e.g. visited a subscription page and left, or added items to a shopping cart and abandoned it).  If you're using Adwords and Google Analytics, you can do this easily with Google Analytics Remarketing, and retarget any visitors on your site based on things like time on site, pages they've visited, and custom events and goals they've accomplished (or not accomplished).