Begin with a fresh sheet of paper, and toss all of your conventional marketing bias out the window. Start as broad and as general as you possibly can. Make a list, including sublists under the main list. I developed a business plan for a company we'll call Acme Model Railroad Supply. Identify the prospect for each objective using conventional marketing techniques.
Every business has some idea of their typical customer, and therefore their typical prospect.
If your product is a consumer commodity, use your existing market research to identify your most likely prospect. The prospect for Acme is typically an 18-60 year old male who is interested in trains. For Acme's retail store, however, prospects are limited by geographical area. Use general Internet user attributes to identify your prospect using the new medium. Match these facts against your perceived demographic.