Many of us actively use sites like Twitter and Facebook to promote our businesses. And those of us looking to connect with more business-related contacts may turn to sites like LinkedIn to develop relationships with people we have worked with or may want to work with. With the growing use of social networking by business professionals, there is a growing number of social networking sites focused on business users and meeting their needs. Here is a list of 20 social networking sites for entrepreneurs, business owners and professionals that are worth a look.