Where to Market Your Kindle Unlimited eBooks

My three fantasy novels and trilogy compilation are currently enrolled in Kindle Unlimited (KU), but I'm struggling with how to effectively promote them. I've noticed spikes in KU pages read when I'm running a Kindle Direct Publishing (KDP) Countdown deal for one of my books, but how should I promote these KU books on their own merit?

I've found a plethora of Facebook groups dedicated to KU, where authors are allowed to post ads for their KU books. I'm not going to list all the sites here, but if you search on Facebook for "Kindle Unlimited" you'll find well over a dozen groups catering to KU readers. For example, KDP Select Authors - Kindle Unlimited Readers is a public Facebook group with over 14,000 members. I've been posting my eBooks on these sites for about a month, but haven't seen any direct correlation to KU pages read yet.

I've found similar groups on Google Plus, but they are less numerous and sparsely populated, so I'm not using G+ to promote my KU books as of yet. There are also lots of websites that advertise KDP Countdown book deals via e-mail and Twitter, but I haven't found any that cater specifically to KU readers.

I'm curious as to methods other authors are trying. If you have any tips, please share. I'd like to reach more KU readers, but I don't know how to do it.

Also, Crimson & Cream is now on sale for $0.99 on Amazon, so grab a copy and spread the word. And, if you subscribe to KU, please look me up!