The new trend is to use social networking models to discover 'influencers' in social groups and use those people's reputations to recommend products to other people. Take for example object (a) versus (b) on page nine of the following paper: http://arxiv.org/pdf/1206.4327v1.pdf
Lindex 'Enterprise SEO Software' has this to say: "Our latest innovation Linkdex Networks enables you to visualise and analyse these groups of relevant influencers. The objective is to enable digital marketers to gradually identify the right personalities and build relationships with them, spreading along those networks for maximum exposure.
If someone within your network has lots of relationships pointing to them you know that they are perceived as trustworthy sources. The aim is to find influencers who are passionate on a niche topic, have strong relationships with the group and are receptive to new ideas with plenty of reach." [1]
It's on fire everywhere in marketing and advertising and there are lots of variations being tried and tested at the moment, and also publicly funded research at universities [2]. Marketers will drop prices online when they detect influencers, in an attempt to encourage them to speak highly of their product to their friends and family (who will need to buy at full price). The Marketing Science Institute has a whole section dedicated to social networks and influencing them [3][4].
Just searching for the term "social contagion advertising" or "advertising influencers" reveals media research arms with nifty tables that map out ways of influencing social groups by targeting information strategically at certain members. For example you can get people to change their view of the "legitimacy of an item" by "encourag[ing] influential targets to adopt the item" or create the idea of a "status disadvantage of not adopting" by "Emphasiz[ing] activities of close connections in a social network to influence behavior". [5]
Perhaps a side note, but the DoD "MINERVA initiative" [6] studies social contagion strategies to track, create or lessen political instability in other countries (although the initiative studies a lot of other things too). The USAID Cuban Twitter project sought to (and nearly succeeded in) creating mass unrest by appearing to be a grassroots movement in Cuba to overthrow the government. You can bet that other countries have these capabilities, or analogues to them, as well (Snowden documents and leaked HB Gary memos show that both the NSA and GCHQ engage in astroturfing and social media manipulation) [7][8][9]. The giant meta-data graph created by the NSA is also particularly valuable for 'influencer' and 'social contagion' analysis.
These sorts of forces are abound on social media websites, as can be seen in the recent Wired article "I liked everything I saw on Facebook for two days" [10]. What's more, the role that social media has begun to play in political races is incredible. If you have the time and interest, look up the capabilities of incumbent Obama's "The Cave" for social media evangelism and tracking. Real time social estimates of support across dozens of major social media platforms with the ability to influence and target any of them at will. Interns scrambling to be "first to post" on online discussions in news media articles.
To be a member of online social media is to be surveilled by both governments and by corporations, to have your content curated for financial purposes, and to have your information sold to the highest bidder. It is also to be influenced not just by direct advertisement, but also indirectly through information that gets carried word of mouth. On the internet nobody knows that you are a dog. This is often an inconvenience and it allows trolls and other unsavory social behavior. Unfortunately it is now also true that on social media, those with the right perspective - those that can see social media at the thousand foot view - not only know that you are a dog, but also know how to make you drool when they ring a bell.
[1] http://www.linkdex.com/blog/social-contagion-why-ideas-and-p...
[2] http://icos.umich.edu/sites/icos6.cms.si.umich.edu/files/lec...
[3] http://www.msi.org/reports/distinguishing-among-mechanisms-o...
[4] http://www.msi.org/articles/what-drives-social-contagion-in-...
[5] http://socialmediaandmobileresearch.com/2014/03/10/social-co...
[7] https://firstlook.org/theintercept/2014/02/24/jtrig-manipula...
[8] http://www.theguardian.com/commentisfree/cifamerica/2011/jun...
[9] http://www.dailykos.com/story/2011/02/16/945768/-UPDATED-The...
[10] http://www.wired.com/2014/08/i-liked-everything-i-saw-on-fac...