It's been my experience that the only way to build a huge, engaged, and paying audience is by building your email list.
If you're starting from zero I recommend you allow for your social network (friends, colleagues, etc) to help you tighten your web based services first. What I mean is to sell, and generate buzz by not selling at all. I'm in the midst of doing it right now. I'm productizing my book. Creating a Fedora based 7 week course with video tutorials. I'll seed my list first with an inquiry. So perhaps 200 people on my Facebook page see the announcement. I will ask them for feedback. I'm launching this product, and I'm very excited about it. What 2 or three things would you like to see in my course that perhaps I've overlooked? Now your community is engaged, and helping you. You should institute some manner to aggregate more emails to your email list when people land on your site. I recommend SUMOME. Simple, and easy to integrate to nearly any email service. So as they register with you, the email automatically passes to your provider.
Dr. Robert Cialdini speaks in great detail how this whole sales process unfolds. Law of reciprocity, authority etc. Now they've helped you tighten your web based service. Now you should thank them. When you thank them, you can give them a coupon to gain access to your web based service at a lower rate. Now comes the fun part. List this MVP version of your services available for a short time (24 hours). Once that's up the sale will close. End. Forever.
1. You engage your audience.
2. You aggregate emails.
3. You generate buzz.
4. You take constructive feedback and improve your product (remove the guess work).
5. You launch your MVP.
6. You offer something that nobody else gets (rewarding your insider friends and family).
7. You close a date around purchase.
While this may not get you 20,000 customers, you will certainly be on your way.
Most important take aways:
1. BUILD AN EMAIL LIST.
2. ENGAGE YOUR AUDIENCE IN YOUR PRODUCT.
3. GIVE THEM SOMETHING TO TALK ABOUT.
4. LIMIT THE ON SALE TIME.