I run a productized service - we have over 20 clients and they all love it. Most of them were found either by posting about it on Facebook groups or referrals - that strategy seems hard to scale.
Congrats! You've solved the first big problem, having a few happy customers who love your product/service.
Questions you need to think about (and the traction book is the absolute best resource I'd recommend to DIY growth).
1. How many customers do you need/want to pick up in the next 6m, next 12m? Without overwhelming your team/resources.
2. If you take a 10X goal, 200 customers, when would you want/expect to reach that?
3. Do your customers have good networks with others like them? If they do then that's the absolute best source for you.
4. Assuming you have a recurring revenue relationship with your customer, how can you touch base with them (on phone perhaps), and actually ask them for referrals? And if they give you referrals reward them with swag/goodies?
5. How many customers do these FB groups have? Can they give you 200+ customers?
6. Does the nature of the end-result you produce give you a marketing advantage? i.e., doing case-studies for each design, posting it on the fb groups, etc. which are value add and not spammy in nature?
Referrals are the best channel, since you will have a warm lead who is looking for your services, rather than a cold lead that has to be educated about your benefits, so I would heavily invest in them.
If you'd like to know more about how you can grow more strategically in the early stage, first read the traction book, and then I can assist on a call if you still need help :)