I will give you 4 ways to monetize and sell your plugin.

First of all, I need to say that you are using social media and Adwords which is fine, but getting the traffic to your plugin page is the challenge. And if you are using social media, are those people in your target market to even want the plugin? They must be WordPress site owners and developers, or otherwise all the Adwords and Facebook advertising will not work.

First Way:

What has worked for some of my clients is to offer a LIMITED version of the plugin for free and then offer an upgraded version for your price on the WordPress repository. That is what the most popular plugins do.

WooCommerce is free, but they charge extra for the add-ons, so that is one way you can go: Offer your plugin for free and limit its functionality and then offer paid upgrades for extra services.

Second Way:

Another way to monetize your plugin is to do what most of the free plugins do: Offer about 50% of its functionality for free and then the other 50% is available through a paid upgrade which is your regular price.

Third Way:
Offer the full plugin for free and ask for donations.

Fourth Way:

This is what I do. Attend as many WordCamps as you can around the country and hand out a flyer or business card with your paid plugin address on it.

I have seen all 4 of these suggestions work for various plugins. I hope one of these works well for you.

If you have any other questions about this, please let me know.

Bruce

I would highly recommend you reach out to influencers inside the WordPress community.

And when I suggest that, I don't mean sending mass emails with pitches.

I mean truly connect with people online and at live events in an effort to build relationships. Once those relationships are built, then you can approach people to review your plugin.

To build your connections, I would recommend:

Attend local MeetUps
Travel to WordCamps
Participate on Twitter
Join Facebook groups for WordPress and help people

I am eager to help people I know, try their plugins, and help promote their offerings. But I have to know them or know of them.

If I receive an unsolicited email pitch from someone I don't know, it goes immediately to the junk folder.

Study how other people do this.

Check out how the plugins WP Fastest Cache + Amped Sense both monetize their free plugins.

Others have already given some valuable suggestions, so I will focus on what's worked well for us.

(To set the context: We have two businesses around WordPress & WooCommerce, 30+ premium plugins, 250k+ active installs)

1. Free plugin on WP.org, and a Pro upsell. Works really well. But make sure to optimize your plugin's description / readme.txt file.

2. Organic inbound traffic - search engines etc. In depth content will get you visitors. This still works!

3. Building relationships - like Rebecca mentioned. If enough people know you, they may recommend your plugins to others - even if they themselves are not the users.

4. Focus on UX, build a better product. There are just too many plugins out there. You must solve a deep user pain to be able to succeed.

Hope this gets you started..

BTW, I spoke about building and marketing WP plugins at WordCamp Mumbai in 2016.. I think you will still find the talk relevant:
https://wordpress.tv/2017/06/30/nirav-mehta-build-and-they-wont-come-wp-plugin-marketing-tips/

All the best!

Promoting your premium plugin within the user interface of your free offering is an obvious strategy for boosting sales. Do not overwhelm your users with too many ads, but do not make it a ghost town either. Place your ads strategically. Use positive language. Keep up with WordPress UI updates.
You can read about it in details here: https://freemius.com/blog/promote-premium-plugin/
Besides if you do have any questions give me a call: https://clarity.fm/joy-brotonath