Another option you have is to look for blogs about your web site's topic. You will already probably know the most useful ones in your field of expertise. Go to those blogs and read some of the posts they have published. If you are lucky, there will be some kind of widget that shows you how many readers they have on that blog for their RSS Feed or email system.
Large numbers are a good sign as that means a lot of people will read the blog and it probably has a good ranking in Google. Read the posts that are relevant to your topic and if you can, write a comment which shows that you know more about the topic. Also, if possible, make a new suggestion or correct an error in the article.
Don't write comments such as "I really liked this post", "Thank you for this information", or even "I really like your blog". If you write comments such as those you won't get any interaction with the blogger in question and you don't add value to the discussion. Such comments will...