Maybe you need to use the WordPress Network feature
Documentation of interest:
EDIT:
Some features of WordPress Multisite based on my investigation:
1 Users can register a blog in your site and publish their pages.
2 Users can embed images, audios and videos in their pages.
3 Users can customize the theme of their blogs.
4 Users can create polls in their pages. (A question and a list of answers)
5 Blog visitors can respond to a blog by comments or by answering the owner’s questions.
6 Users can create/delete a list of visitors for their blog. Visitors should have basic infomation such as name, email and auto-generated passcode. (For example, a blog owner might want someone to enter a passcode to view a certain page of his blog)
To get started and to learn more, go HERE
Also, check out BuddyPress, a WordPress plugin that will allow you to build your own Social Network