On the topic of creating social media profiles, it is not just about using Facebook and Twitter, or using as many social networks as possible. Granted, Facebook and Twitter are 2 of the most popular sites with the most traffic, and are safe choices to start with.
However, its important to think about which site will most of your targeted audience use? If you're a ecommerce retailer, Pinterest is a good way to get your products known, repinned and shared. If you're having a B2B business, LinkedIn is a good way to get your product known to business professionals.
Ultimately, social media marketing is more than just "creating" profiles. As what other forummers have mentioned above, you need to plan out an engaging content strategy for them, and not just plainly use it as advertising tools.