Yes they absolutely work.  But you have to make sure you have the right goal for your ads and that you are measuring the right things.

Facebook has some of the most highly targeted, lowest cost per click advertising available on the internet today.

Facebook ads do work differently for different industries and will take testing, patience, and more testing.

It’s also important to note that if you have a low-cost product like an e-book or a £3 product, it’s very hard to have a positive ROI with Facebook ads.  You can use ads to drive traffic and get more brand awareness but you may need to vary your strategy with other methods of organic reach on Facebook.