A question that your business must answer, "Who wants to buy my stuff / services?"
The first step is always to define your audience and determine a keyword search that they would be listed under, like "cancer treatment", or "antique jeep".
There are a few online tools that will help you to define and track those customers in new ways.
Search for lists or people who use Twitter to discuss your subjects.
Placeblogger is a tool that allows you to find all the blogs in your local area. It allows you to more easily find the pulse of your market, and also serves as a list of people to approach who could push your new product or service.
This service allows you to upload your email contact list from your local computer or several online tools. It returns job titles, demographics, an online Klout score and what social networks they use.
You can get 100 free, but then you have to pony up.
Be sure to also follow up with specific people that you personally know who match your target. It never hurts to ask for a favor from a friend or aquaintance.