Most small businesses have no paid employees. For the state of Michigan, over half of all business establishments have fewer than five employees. The Small Business Administration provides regulations that determine the size limits for "small" businesses. A table of these limits for industries can be found here. The limits are given in revenues for some industries and in number of employees for some. For example, establishments in mining have employee limits of 500, while those in transportation manufacturing have limits of 1,000 employees.
Simple explanations of the economy or job growth generally miss the mark. But politicians often look for simple explanations and simple solutions. Promoting small business will not solve the employment problem. A better solution is to provide an environment that supports business activity regardless of the size of the firm.