Unless you're living in a cave, you can't help but notice the impact of, or at least the buzz about, social networking sites. As you might expect, large percentages frequenting these sites are the younger generations, teens, high school and college students, and young professionals in their 20s. One reason, why agencies care about these sites, is that all types of businesses are exploring how they can take advantage of these new methods of communication. Using the sites as a marketing tool requires an understanding of a marketing technique called viral marketing. Viral marketing and viral advertising refer to marketing techniques that use pre-existing social networks to increase brand and product awareness. Here's how social networking sites work: 1. Go to the Web site and sign up for a new account. 2. Create a profile that captures information about you. 3. Invite friends to link to your profile. 4. As people accept your invitation, your network grows.