The answer lies with your existing customers.
There are hundreds of ways to try to make it easier for new customers to find you: from online advertising and SEO, to traditional print and broadcast advertising, to billboards, listings and even cold calling. What works for you will be very much dependent on the nature of your business.
However, the way your current customers found you will very probably continue to work for new customers. Fortunately, you know how to contact your existing customers – so ask them how they found you.
As a bonus, by engaging with existing customers you’ll also encourage word of mouth recommendations, which is still one of the best ways to generate new custom.