I recently launched a Kickstarter campaign and I use Facebook Ads (only) to promote Post to my facebook fans. Facebook algorithm shows publications only to a small percentage of your audience, so it is important to reach everyone. For relatively little money you can make that posts reach all your audience. It will be displayed whit the tag "advertising". I recommend using this kind of advertising.
Regarding reach an audience that does not know you directly is risky and expensive, but I have not tested much.
I hope you had more luck than I did. I've spent about $200 on FB ads. I tried many different campaigns and strategies. I was getting website clicks for $0.02 and drove thousands of visitors. I got back a single FB pledge, for $15. Who knows, maybe the ROI is down the road. Part of the complexity is there is no way to place a facebook tracking pixel on your Kickstarter page. You can point traffic to a special page on your own website, then to Kickstarter to get detailed feedback on which ads are working.
Facebook lets you upload a list of email addresses from previous customers. I did this and served ads to 170 people who have bought my photography via PayPal. Zero Kickstarter pledges from that.
Now, I can't blame Facebook ads, but my experience was low return. I would love to hear about some Facebook ad success stories. Has anyone seen one?
I've only ever found Facebook ads effective for recruiting new followers for my Facebook page. I did have some luck driving people to Kickstarter from my FB page though, so I suppose the ads would have been better as a pre-campaign project to build up my audience there.
I have a feeling that this sort of thing may vary by type of product. A day or two of ads can be a relatively inexpensive investment. (Even less if you can find a discount code for the ads.)