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 :)