It doesn't matter if this site have been in existence before my site enters into the online fold. Remember, all this siye you mentioned based on a specific niche. It doesn't mean everything they post is same as yours. You might base on your own niche and post different from theirs, and yours will be listed on top base on your keyword which is preferred choice by search engines.
Well, I have tried this with the blogspot blog I think and it did not rank at all until I searched for it specifically. Even though, my blog had some article, it still did not rank well. This is why I believe that social media marketing is best for promoting a site rather than goin after search engines but it might be possible that I was not good at SEo and this is why my site was not ranked well.