I love this!
So I am a marketer by trade, web developer and MBA.
I don't know about getting users being the main issue. Consider things such as your target market, often times businesses i work with strive and invest in one group to only reach marginal success, then after some evaluation and pivoting to another (better) group the business just takes off. So target and how you approach them is key.

As far as growth hacking - well, I have growth hack a few platforms and the main thing is that you have to have some traction. GH is not a replacement strategy for traditional/digi marketing. You need to already have some traffic to grow it..the hacking part is simply expediting the growth.
With that said, GH is a combination of efforts from PR to press releases, to the flow design of the websites, having perfectly crafted landing pages (one for each possible target customer you might have) running AB testing, finding out who your personas are and targeting them through social networks (not all social networks are right for all personas - hipsters are better found on instagram than FB, while your demographic is probably on facebook & facebook groups but you can leverage both insta and fb) and measuring your bounce rate, among other little things... Growth Hacking is about focusing on a lot of little things at once... Is relatively cheaper than marketing because you have to hire one person and or pay for that one person versus paying for the service time on top of the print/marketing materials etc... so GH is cheaper as well but not completely free either.

Think of it as a colander you need to get as many targeted individuals, each person gets send to a custom message landing page with just the right content for them, some will seep off some will give you what you want (email, subscription, referrals,etc - landing pages shall have just one goal) if you make it past that phase, they are followed up with emails or phone calls or are directed to your site or fb, etc.. some will engage there some don't - seeping off through the colander...lol. once in your page you might have an email subscription again just in case. Ads on google can be placed and be used to direct to landing pages or a specific place in your site - same as FB ads. One thing on instagram is to not post pitchy images all the time.. have people like and follow funny non-intrusive posts with just the right tags (again, your target demographic there) then once they are already following you once in a while you post a sales image or comment.

There's more to it but I hope this gives you an idea on how to get started. If you would like to hire me for either landing page creation, web modification or GH services message me :)

Consider creating a kickstarter style interface with the new properties being the 'campaign'. You can almost follow the entire system and apply it to your model.

I have a background in developing disruptive technical solutions in the Real Estate training space.

Launching a new web platform is nearly always a challenge. Generating the initial momentum to get a marketplace up and running can be very difficult. I was recently part of a successful website re-launch so I will outline what worked in this particular case, although, admittedly it may not be the best strategy in all cases.

The website in question had actually launched a year before we started promoting it. During this period the website languished with very few users and little traffic. The concept was sound but it relied on obtaining a significant number of buyers and sellers to create the momentum necessary to make the website a viable experience. Without these users the website was a waste of time and energy.

How we did it:
Step 1: We narrowed down our market to a single city, or actually a region. We chose the greater Seattle because it is a very tech savvy city with a number of early adopters. This allowed us to get enough items listed and enough people looking in a geographical area. It also allowed us to focus our search engine optimization so that when users started hearing about our platform and started looking they were able to find us.

Step 2: We dedicated 5k to search engine marketing focusing primarily on Bing and Google. This marketing was carefully designed to target potential customers for the site. We tracked each click in detail and recorded the percentage of those clicks that turned into members and of those that became members how many completed an action. We spread the 5k over 1 month and collected as much data as possible on those users.

Step 3: Near the end of our search campaign we did a detailed press release of the launch of the new site. This was something that wasn't done before with the original launch. With the press release we focused on reaching out to media in the Seattle area. We targeted publications and writers who cover local start-ups and similar industries. We were able to get a couple of nice write-ups in local online and print publications that lead to further membership growth. Our data indicate that one of the driving factors in these users joining was the fact there was visible activity on the site from our search engine marketing campaign. It is our belief that had we not created that initial activity that the press campaign alone would've been insufficient.

Step 4: We produced a detailed presentation that demonstrated that every dollar spent on search engine marketing led to $3.40 in sales with over $2.50 in direct profit within the first 60 days. We took this presentation to potential investors. Since we had real data proving that we had created a viable model and momentum it made investment a no-brainer for the right investor. Most of this investment was turned into marketing dollars and spent on a larger search engine marketing campaign.

Step 5: We are continuing to use data to fine tune the operations of the website further increasing sales. We have also begin to expand into other markets using a similar strategy of of initial marketing, press release, continued marketing. We have also began to see the benefits of search engine optimization and referrals from other users. We have instituted other methods including a referral bonus system and a social sharing point system that have both helped drive further growth.

While is certainly not the only way to launch a website, this is one way that can work and in our experience it worked very well.