Though the Internet is made up of tens of millions of web sites, people spend the vast majority of time on just a handful of them. According to comScore, an Internet analytics company, Americans spend most of their time online on Facebook -- 10.8% in December 2012. That month, Americans spent another 10% of their Internet time on Google properties, including Google search and YouTube. Based on comScore's report, "U.S. Digital Future in Focus 2013," 24/7 Wall St. identified the 10 Web properties where people spend the most time.

Many of the top online sites have managed to significantly increase the time spent on their sites in the past year due to the rise in mobile devices, such as tablets and smartphones. The top 25 digital media properties in December 2012 increased their reach through mobile channels by 29% compared to December 2011. Some increased significantly more than that. ESPN expanded its digital reach by 56% compared to 2011, more than any of the 25 largest online properties except for Pandora.

10. ESPN

9. Craigslist

8. Tumblr

7. eBay

6. Amazon

5. AOL

4. Microsoft

3. Yahoo!

2. Google

1. Facebook.com