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.
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.
Include details about all of the following that are applicable to your business in the marketing section of your plan: location and distribution, and promotional strategies, such as packaging, public relations, advertising, and customer service. As a result of exploring these areas, you will naturally need to consider how much you will budget for your marketing efforts. This question is closely connected to your sales forecast, which leads us into the next section of the business plan.
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.