Welcome to the community. I bet it's exciting and frustrating to launch a new community.
So a few things I'd be looking at here:
1) How can people find the community through your site? I visited but couldn't see any obvious link to the community - only the existing help center. This is probably the biggest challenge at the moment. It feels like internal support might be a little low if it's not featured prominently from the homepage.
2) Assuming it's a support community, when you emailed people to join what did you ask them to do? If you tried a big launch and it didn't go well, you might want to work at the micro level first. How many people opened the email, clicked the message, visited the registration page, and completed registration. That will tell you why most people dropped out.
3) Looking at the community, I suspect there might be a community concept problem. Do people that use the product want to know how to sue it better or does it work well enough? Do they feel an affinity for others (i.e. do they want spotlights from other customers? What did your research tell you?
aside: If you're trying email, facebook ads, and word of mouth strategies via CSMs and it's still not working, it's probably a concept problem. The current concept isn't strong enough. One community to look at here is Unbounce's by @justin_veenema_1 (or @justin_veenema). They also use Discourse and have a pretty active and engaged site.
4) The product AMA seems a little self-promotional and doesn't include questions from members themselves . Actually a lot of the posts here seem very much about selling Callrail than having a sincere discussion
5) There are a lot of posts with no responses. This will discourage participation from others. I'd remove or replace them.
6) Do you have a small group of people you have strong relationships with initially you can engage and facilitate activity until others arrive?
7) I'd consider taking the most common questions from customer support lines and answering them in the community as well.
At this stage, I'd prioritise tweaking the community concept, highlighting the problems you can solve for customers, promoting Callrail less, building a small group of people to engage initially, testing different appeals by the mailing list, and driving traffic from the main website. You definitely need more than 101 users to make this work.