In addition to what Post #2 says, there are things like Groupon that rely on customers to pass along messages through social media. In Groupon, a deal is offerred only if a certain number of people take advantage of it. Therefore, if you want to get the deal, it is helpful for you to encourage others to do so as well. In that way, the job of advertising is in someways being passed on to the consumer. You can also see this with firms encouraging people to "like" them on Facebook.
One of the most significant new trends in advertisement is the use of social media. Businesses large and small are using the internet and the power of the masses to get the word out about their product. Businesses regularly use Facebook, Twitter, LinkedIn and YouTube to use and grow their customer base. Businesses can put their newest commercials on YouTube and let their money go further. They use text messages and Twitter to send updates and promotions. Businesses have been very creative in their use of Facebook for advertising.
One of the advantages of social media is that it is far less expensive than more traditional advertising methods. It is also flexible and has much faster turnaround. A disadvantage is that these methods can be more intrusive and may alienate some customers, so companies have to use them carefully.