This is just my opinion:
I think Twitter and Facebook are great but not sure that is the best place to start. With the various CMS choices out there, 9 times out of 10, someone who is going to start a site is going to seek the advice of someone who has experience in the field. I get asked all the time by non-technical people what CMS they should use. I can recommend Jamroom to non-technical person, but if 9 other people are saying Wordpress, then my suggestion isn't worth much. Technical people in my opinion should be the primary focus - a primary focus based on building the referrals by web designers and developers. Competing in the open web against other major offerings (Wordpress, Joomla, Wix, etc) is like the taking on the US Navy in rowboat with a slingshot.
Coming up with a concrete comparison chart and plan to win over the technical people on sites / forums that are technically focused would be a great plan of attack. Maybe having a promotion for developers where if they're a registered business they can get a free license or something. This would also give you a valuable database to market too and allow mom & pop web development businesses to look at switching over to Jamroom from Wordpress. Give the mom & pop web development a reason to switch to Jamroom.
Building clients sites with Wordpress I see all the time, we need to them to start using Jamroom as their default CMS instead of WP. Jamroom has everything needed for them to create a quality robust client's site. Since most of the key modules are developed and maintained by the core Jamroom team, this would provide for better security then a bunch of plugins from an unknown Wordpress developer. You're new pricing structure is also a key advantage. You offer A LOT for the price.
Having bullet point facts about why Jamroom is the better choice is necessary. Those facts would need to be competition class, not a casual comparison. Win those people over with a better sales pitch with concrete facts and they'll start moving to this platform and telling other non-technical people to use Jamroom.
Jamroom has A LOT to offer. Key points would be datastores, the excellent choice of Modules, form creator, Aparna, Groups, and Site Builder. Most of the people I know have never heard of Jamroom. They're all using Wordpress to build client sites.
Searching Google for "major cms systems" or related terms, finding people who review CMS systems, and sending them a pre-written email about Jamroom would be a good way to spread the word and get inclusion on future articles. It's also important to start following these same people on twitter and using the correct hashtags to impact people who are working with CMSs.
I try to promote Jamroom to anyone I come across that wants to use a CMS. It would be wonderful to finally run across someone who says back to me "I use Jamroom and love it." That hasn't happened to me yet and I manage over 20 twitter accounts in various industries. Besides this site, I haven't had a technical discussion with anyone about Jamroom online, with the exception of Centmin Mod forum.
Some other suggestions would be to:
1. Start a Jamroom Slack channel.
2. Setup a Jamroom Reddit page.
3. Submit to Product Hunt.
4. Create a thread on WebHostingTalk.com.
5. Post on HackerNews.
6. Upload Jamroom Core to Codecanyon.net as free.
7. Start some kind of promotion to get people to test out Jamroom like a Hackers contest with cash prizes. "Jamroomhack" every June XX to XX. Come up with the best module in these categories and win $XXX in prizes. Do this every year.
I found out about Jamroom in 2006 on Hotscripts.com. That's where it all began for me.
Maybe you're implementing some of these suggestions already, I don't know. But if you win over the developers and web designers and you'll have a ton of people using Jamroom for a wide variety of purposes. Those developers in-turn will recommend Jamroom to other people who are looking for a CMS to use. We're social creatures and often times seek a more knowledgeable source for a recommendation. Win that recommendation and Jamroom wins.
updated by @jimmy: 06/17/16 08:52:47PM