I tried FaceBook ads for some of my titles, each being presented by its front cover and its blurb in my FB page "Jean-Paul G. POTET, author". The principle is very simple. You select three criteria: age bracket, area, interest. The basic campaign costs 18€, but is actually charged 20€. It runs until the 18€ are spent. The FB ads search engine looks for potential subscribers interested in the product you are promoting. For my title "Spiffies and Loonies", the criteria were 13-65+, USA, books. Whenever some FB subscriber clicked on my ad, I was charged a fee that varies constantly, but is often about 0.25€. Until recently, FB showed the graph of the people who had responded. Some teenagers were interested in my book; the curve reached 0 in the middle-age range, and soared among older generation. A similar test for the French version (Fringues et Dingues) limited to the French readership showed a steady increase in interest from teenagers to old folks. I have spend about 80€ to test four titles, but I am not going to continue because the discontinuation of the graphs is a big disappointment. I started all this in December 2018. So far none of the four titles advertized has sold a single copy. Let's wait and see.