Social networks are not channels for advertisers or for the adverts/memes you, your clients or any of your so-called "influentials" create, social networks are for all of the people who participate in the network.
Being a social creature means you spend your life in social networks; being part of a social network gives each individual a number of benefits - shared protection, shared resources and most importantly shared learning. Our ability to learn from each other (the appropriately-named Social Learning) is one of our all-too-mutual species' most characteristic capabilties and the engine by which stuff gets pulled through populations (from technologies to health habits)
Social networks are not best understood as channels down which folk send things; social networks are webs from which members pull down learning (from each other).
one for all my marcomms friends :)