We are just about to launch an online marketplace with a focus on waterfront lifestyle living.
My agency and I have helped countless startups reach their target audience and get their foot in the door. There are many things you can do: social media marketing, google adwords, promotions, print advertising and even getting content published in residential magazines.
I would love to help you in more depth - I own a full service marketing agency that offers all types of design, branding, consulting, marketing and content services at reasonable prices that won't break your budget. http://www.bloominari.com I also can give you a project estimate for free: http://www.bloominari.com/contact/request-project-quote
It's all about researching your target audience, monitoring competitors to know what works, reaching your audience correctly and speaking to your audience in a language they understand. Let me know if I can help you in any way and best of luck to you!