Studying your market will give you insight as to how you can make your business more appealing to people. Market research is more than just noticing trends in your customers' buying habits; it's discovering what motivates your customer to buy. Don't assume that you already know because you've been in this business for years. This study often unearths characteristics about your market that are hidden or new. It's best to discover these things before your competition.
Personnel: The success of any company depends on their ability to recruit, train and retain quality employees. The amount of emphasis in your plan for this section will depend on the number and type of employees required.
So, although a detailed business plan may not be required for an online business, I am going to include it here so you can at least look at and consider each section and determine yourself if it applies to your business.
If an online business, you need to go into detail how you will attract customers to your website. General statements like "I will use Face Book ads and email marketing" will contribute almost nothing to helping your cause unless you have detailed statistical analysis of tests you have conducted or of another similar business you have been associated with. If you do not have any data upon which you reference your estimates, it could show lack of proper thought to the remainder of your business plan.