Here on EnlargeYourPen you are able to connect to Blogs and Authors to build up high quality relationships mainly for guest posting/guest blogging opportunities.
You can register on this site as a Blog or as an Author.
AS A BLOG you are able to create jobs. That means you (as a Blog) offer someone (an Author) to publish an Article (Guest Post) on your Blog. When you post a new job you can specify everything that is important to you. Of course obvioust hings like the topic but also more in detail stuff like minimum words you require or a deadline that you might have. You can be as specific as you want to find the best match for your job.
AS AN AUTHOR you are able to apply for jobs. That means you (as a Person) offer your expertise in form of an article to be published at a blog.
Both, blogs and authors can set up a profile to show what they are specialized at and can be contacted directly by mail.