There are many sites online that are great for authors and enable us to market our books to a much wider audience. In particular sites that encourage you to announce any kindle book free promotion that you do.
If you sign up to the KDP select program then you are able to promote your kindle book for up to 5 days free promotion in every 90 day period. This is really worth doing especially if you have the opportunity for readers to sign up to your email list by offering some free gift in your kindle book.
One of the sites that I recommend you use to increase visibility of your free promotion is Author Marketing Club. Here is a video showing you how it works. You can sign up for free or purchase a premium membership.