You generally shouldn't start communities to attract new customers.
The only people that join, are people already in your audience (typically your customers).
Why would people that don't already purchase the product/service participate in a community about it?
Yet, there is an exception. Imagine if you sell high-price products and services (consultancy, most business services, homes, cars etc…), the potential value of each individual participant in the community is high (see the amazing value of B2B communities).
Instead of developing a community around your data security consultancy services, you can develop a community about data security. You invite the people you know in the sector to participate, gradually they invite others and it begins to take off.
Through this community you can identify potential leads. You can identify problems members are having and drop them a note to see if there is anything you can do to help. This doesn't scale, but it doesn't have to given the huge value of each person. If each participant is responsible for $50k worth of services, it is a valuable activity.
How much easier would it be cultivate and convert leads generated from a genuine discussions compared with cold calls. How much more credibility would you have being the founder of the community compared with other channels?