A sound, written plan for your business should have two perspectives. First, it should be a working document detailing how you plan to succeed with your company. Second, it should be a sales document, a tool to attract capital funds from various sources. All businesses need a written plan, even if they're not just getting started or trying to raise capital, because management needs a written document against which to judge progress. What do investors look for in a plan.
Most professional investors have a pile of plans on their desk.
Your first task is to ensure they read yours. How do you select a new book at a bookstore. You take it off the shelf and start to read. Investors react the same way with business plans. Otherwise they won't.