Only 1 person mentioned influencers. I'm going to recommend it again, but with more detail.
An influencer has a particular niche/segment in the market that they are passionate about. They may have various channels in which to communicate to their audience, these may be facebook page/groups, youtube channels, instagram.
These influencers have from 100 to 100k audience members. There's nothing you need to do, apart from approach them and to find whether it's a good fit to pitch your product. However, be aware that the influencer will be looking for a % of sales.
What is great about an influencer, is that in some cases they did all the hard work for you. They already created a product that the audience members consumed and are generally happy with it. So if you have an addon product, then you are simply preaching to the choir at this point.
Where to find influencers? Youtube, Facebook Groups, Instagram. [1] Is a place to go, if you want to be laser targeted and have stats.
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Now for anecdotal experience. I'm in the affiliate marketing arena. I know many many different influencers. They either have products developed for them or they cross promote each others products.
These guys regularly generate from around $10k to $100k a month. I've met few that have done $1m a month in sales.
Done correctly, you can position yourself to flip a switch and have over 1m unique users read or hear about your product.
I know there is a segment on HN that generally frowns upon affiliate marketing, but many companies such as Netflix, Groupon, AirBNB, Apple, Amazon used them to great effect to grow exponentially.