Hi there,
My site is  ranking well for my site on Yahoo, but it won't show my title tag or description tag in the search ranking result.
I have implemented the WP SEO Plugin. Any help would be appreciated in this matter.

Had you tried the same in google?

In my opinion.You can try manually work for your title tag or description tag.WP SEO plugin is best but it will take automatically your title tag or description tag, so you can try it manually.Its really get the good result in the search ranking result.

google that problem u will get solution

Wordpress - It's an SEO friendly platform, Nowadays most the people who preferred WordPress for developing their websites.