I have released two of my three novels as audiobooks this year (still looking for the "right" narrator for novel #3) and while I am pleased with the final product, there is a significant downside to producing an audiobook: marketing it!
Audiobook Creation Exchange, aka "ACX", is a great tool for authors and narrators to get together and create an audiobook. ACX also looks after the distribution of the book once it is finished, through their own subscriber based customers on Audible, as well as through Amazon and iTunes.
On the surface this all looks great, and for the most part it is, but there is a major pitfall: they offer zero advertising. Unlike Amazon's Kindle Direct program, which allows indie and traditionally published authors to advertise directly to Amazon's Kindle Unlimited subscribers, ACX has no such program. Sure, your book is advertised on the Audible site, but it can quickly get lost in the large number of competing audiobooks.
Even other paid advertising sites, like BookBub (which is one of the most effective - and expensive - advertising sites for authors) do not offer an exclusive audiobook advertising platform. This makes things difficult for indie authors such as myself to get the word out that their novels are also available in audio format.
Surprisingly no such paid advertising service exists, at least that I have been able to find. Even more surprisingly, neither Audible nor ACX have a pay per click advertising service, yet each are owned by Amazon who makes a significant income from the same service for print and e-books. There is definitely a market for such a service, and the lack of such a service is lamented heavily in online forums.
So what is an indie author to do to advertise their audiobooks? For me, it means that I have to try and work mention of my audiobook into my regular advertising whenever possible. This is not the most effective way to advertise - it is always best to target your market carefully, and e-book readers are not generally audiobook listeners - but something is better than nothing. I also make sure to regularly update my social media feeds with mentions of my audiobooks, especially when they rise up in the ranks of their respective genres.
It is frustrating to have two very good (IMHO!) audiobooks on the market and minimal ways in which to inform audiobook listeners that they are there and waiting to be enjoyed. Such is the life of an indie author...but I still wouldn't trade it for the world!