There are many ways to determine which efforts are producing results and which ones aren't. For example, you can study your website's analytics through your web host or by using Google Analytics. Most social media sites provide analytics as well, or you can use tools such as Hootsuite to get social media analytics. Your email service should also provide you with information on the open rates and engagement rates for your emails.
While SEO allows you to optimize your website for a greater chance in appearing higher in search results, and online advertising allows you to send promotional content to the target audience of your choosing, SEM combines both benefits as your content is both optimized for higher search rankings and is placed primarily in front of audiences who are most likely to convert when they click on your ads.