You mention that marketing and promotion is not one of your strengths. I.presume none of the 5 cofounders is a marketing guy. Maybe getting a marketing guy on board can bring clarity to the process of bringing customers to your website. Having said that, its not necessary to having a marketing specialist. Make a list of all potential traffic sources - eg googladwords, facebook ads, stumble upon, ads on forums and test them all out to find which works for you.
If you can mention what your business is maybe others here can help you with a marketing strategy
If you can mention what your business is maybe others here can help you with a marketing strategy