You need to “go wide” as I call it. You need to try a lot of approaches. Here is where I would start:

• Network. Go to events. Go to tradeshows. Talk with people and explain the value. Collect email addresses or business cards. Follow-up with people (store these relationships in a CRM)
• Don’t be shy to reach out to people. Start emailing, calling, sending LinkedIn connection requests.
• Start a compelling blog. Or podcast. Get industry relevant people to guest blog/podcast with you. Try to get on other blogs/podcasts
• Get reviews. Get the product out to as many relevant review sites as possible
• Publish specific usecases. Make sure they are targeted and actionable. Make sure the value proposition is clear.
• Get PR. Reach out to niche specific outlets. Blogs, podcasts, local media. Anyone who will talk with you. Start publishing those articles on your social media.
• Engage on social media: Get active in relevant Facebook groups. Get on to LinkedIn. Get on niche specific forums. Follow and engage with relevant influencers on twitter.

Most importantly of all, when you get your first couple users. Treat them like royalty. Roll out the red carpet. Try to absolutely go above and beyond. Small businesses grow because of word of mouth. I will say that twice just for impact… small businesses grow because of word of mouth.