Social media are websites where people interact, share and discuss information about each other and about their lives. At these websites, individuals and groups create and exchange contents. They appear in many forms including blogs and microblogs, forums and message boards, social networks, wikis, virtual worlds, social bookmarkings, taggings and news, writing communities, digital storytelling and scrapbooking, and data, content, image and video sharing, podcast portals, and collective intelligence. There are lots of well-known sites such as Facebook, LinkedIn, MySpace, Twitter, YouTube, Flickr, WordPress, Blogger, Typepad, LiveJournal, Wikipedia, Wetpaint, Wikidot, Second Life, Del.icio.us, Digg, Reddit, Lulu and many others.  Social Media has led to even cause naming of this period as Social Age, according to this list in wikipedia  which is by itself one of the main social media websites.
As one of the most widely used social media, the social networks are becoming more popular. According to several statistics the popularity of Facebook alone, has reached about 900 millions.  This huge number of users of social networks in general, triggers a very important question about their impact on societies. Actually, some people claim that these sites are beneficial for society, but others contend that the dangers of social networks outweigh the benefits. Let us discuss the both sides.
Social Networks have several advantages to consider:
1- Social networking sites help people to create new relationships and reconnect with friends and family.
2- Social networking sites help people to make groups with those who have common interests together, offer a community to build new ideas from around the world.
3- Social networks can lessen the social anxiety for those who find it difficult to speak in person, because people who have difficulties in communicating in person are more comfortable interacting on the Internet.
4- These sites can help with major life issues such as changing jobs, finding a new place to live, buying a car, etc. Because social networking sites help people to connect with friends and experts who can assist in their decisions.
5- As a very interesting thing about social networks for me as a student, students can use social networks to discuss education related topics. A research shown that about 59% of online students say they talk about any education related topics, including college or college planning, learning outside of school, news, careers or jobs, politics, ideas, religion or morals, and schoolwork.  This research happened in the year of 2007, it is natural to think that this percentage has increased now after five years.
6- Social networks can be a powerful tool for social changes and an alternative to more traditional methods of communication. There are many of relevant examples of this role of social networks. For instance, many people got the information they needed about political campaigns in the United States in the latest and the previous elections from such sites.
On the other hand, like everything, social networks have disadvantages too:
1- Social networking sites attract people to spend more time online and less time interacting face-to-face. This is because these sites contain many time wasting activities that supplant more productive activities.
2- People who use these sites frequently are prone to social isolation. Parents spend less time with their children even when they live in the same house, because they are using the Internet instead of interacting with each other.
3- Consequences from over-sharing personal information include vulnerability to sexual or financial predators. That is why it is always advised not to share much personal information on these sites. In fact, about 25% of facebook users do not bother with privacy settings. 
4- Social networking sites have no way to verify that people are who they claim to be, leaving people vulnerable to solicitations from online predators who are able to mask their true identities.
5- Social networking sites make cyberbullying, a type of bullying that occurs online, easier and more public than bullying through other online activities such as email and instant messaging.
6- Social networking sites were created to make money, not to improve peoples’ lives. These websites use networks of online friends to accumulate data about people for the purpose of selling advertising. These sites place cookies on the users’ computers, gather information, and track interests to show personalized ads. These advertising practices may constitute an invasion of privacy.
In conclusion, as it is shown above, there are different pros and cons of social networking sites on the society. As an important thing to remember, overdoing something is always wrong and it has more disadvantages than advantages, and this is also applicable on using social networks. We can make them more useful when we just use them for good reasons for just less hours daily. There is no necessity to stay for long periods on some social network.