>>510 (OP)
You have to do something unique to make it popular. Look at reddit. It's basically a text board where OPs are encouraged to contain links to other websites. Before that there was Usenet. If you want something popular or original, you need to think:
What did Usenet do?
What did 2chan do?
What did bulletin boards and web forums do?
What did Reddit do?
What did Twitter do?
And maybe you'll come up with something interesting.