First find one by searching for relevant keywords, like keywords you use in your own posts/pages/content, then use opensiteexplorer to find out what sites link to it. Or some other tool.

Other method is to set a google alert for your niche keywords.

Get scrapebox and fish out recent blog post in your niche and then leave useful manual comment.

There are lots and lots of video tutorials to show you how to use it either by searching Google or YouTube..

I usually start with those that I continually see are out-ranking for me for the niche I'm in.

Joey

I have found the blogs I regularly visit firstly by using Google and then by blog hopping. So when I find a blog that has a nice amount of comments I check the blogs of the people who have commented. Then I do this again with any other interesting blogs I find. Apart from traffic it's been a great way to form relationships with other people in the business.

This should help... Google Blog Search

I think the best way is to it manually. You can use Google anytime and search for blogs with the same niche as yours. Then put a relevant and useful comment.

If you can't buy scrapebox or similar, can get qbf for nearly $11 (finds contextual blogs - keyword based - that have been recently updated).

Here's a few techniques for doing proper searches.

By using search operators, you can find much better results when doing your searches.

Enter these into the search engine field:
inurl:<keyword>
intitle:<keyword>
Site:.com

Example:
You want to find blogs about the 2014 Olympics.
Use something like:
olympics site:.org intitle:2014

Reason: 'olympics' is a regular keyword that you might use in a search. Blogs are often, but not always, on sites with .org tld's. Maybe you want to limit your search to sites about the upcoming Olympics of 2014.

Also, you may notice that there are certain common terms used within Blogger, Wordpress, and other platforms. You can further narrow it down to those platforms. Off the top of my head, I can't recall the common terms to use.

You can also use the Google blogger search.

Some folks have automated their searches, so...yeah. No need to purchase anything necessarily.

You need to study google keyword identifiers, this will be your greatest help and you can search for the ones you can post on if you

Heres a cheatsheet for you.
Big List Of Google

Just try Google Alerts. All you have to do is type your desired keyword on the search query and set results to "Blogs". In that way, once you receive alerts to your email, you will see some new or recent blog posts that are published, amnd may consider them as active.

Google alerts works well for me.

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If you need a bulk list then get scrapebox and scrape using keywords. The keywords I found quite useful are using your keywords and then a date. Go back the last few weeks. E.g. "dog walking" +"1st September 2013", etc.

Google Blog Search

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Find someone on fiverr to do the leg work and find active sites and maybe get them to comment too save you time

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The first step should be search good and relevant keywords. Those keywords which you can put your forums, blogs, articles etc, it needs to be applicable.

Because keywords and blogs are the major part in any site. You also need to choose an interesting topic which would help you to increase your readers very frequently.

If you need to judge, that your keywords are appropriate or not you can set a Google alert for your keywords. For getting active niche blogs to comment on and more viewers for your post you need to create more traffic for your site.

For generating traffic there have lots of methods like social media, blog commenting, forums commenting, article marketing guest blogging etc. Facebook Twitters, Google+ are the tools of social media and marketing and these are best techniques which can help you to reach your target audience easily.

So go and use these methods and I am sure you can reach your goal otherwise you can consult with any professional guys.

Search Google for blogs in your niche. When you find one, check to make sure that it is already getting comments. You can then read the post and leave your comment.

Click some of the other people's blogs that left comments and from there you will start finding several blogs that you can leave your comments.

Just be sure to take the time to leave useful comments, otherwise you risk the chance of getting your comment blocked as spam.

Is there a way to check which blog recently approved comments? How many comments are there on particular url?

Like, if i have a blog which 2 days back approved comment and it got only 6 comments. Chances are the owner is reading and approving comments? Any tool, which does this?

I use site called dropmylink.com , it is connected to google and instantly finds the best .edu , .gov and other highly ranked blogs that you can comment on.
Don't spam though
Art

I use dropmylink.com You can find tons of different sites to blog on. My favorite type is the comment luv blogs.

I'm going to throw in another vote for Google Alerts but I want to give you a secondary reason why to do this: You want to set up multiple ones so you can get an idea as to what the "supply and demand" of that word usage is lately.

For example, I have an alert for the words "guest blogging." In the months of February-mid-June, I got in the ballpark of about 6 emails a day. It was almost annoying. Then, when the whole no-follow link vs. do-follow link war went down back in late June, it got to a point where I went an entire week without seeing an email. So just by having the alerts, I was able to take the temperature of the terms. Now, I have seen it back to where I'm getting about 3 emails a day with multiple links. It's just interesting to say the least...

You could as well use footprints. e.g search "keyword" powered by wordpress to get wordpress blogs in that niche.

You can use this search phrase on Go0gle to find blogs with a higher quantity of comments :

"niche keyword" "30... comments"

Ex. "gardening" "30... comments"

It shows blogs with a higher quantity of comments. The 30... can be changed to a higher or lower number if you want to change it.

What this means is that there are at least 30 comments on an article.

This is a reliable sign that comments are either open or that the webmaster is approving their comments on a regular basis.

OR

--- Use Reddit (dot) com and find the sub-reddit for your niche. Example:
Gardening, Plants, and Agriculture. (over 58,000 people reading and
posting stories on Gardening topics).
There will be a number of very popular blogs mentioned repeatedly that you should check into and see if you can leave some quality comments on (with your link of course).

30 is fairly high unless it's a REALLY popular blog with a lot of activity.

Like everyone is saying, Google is your biggest friend for finding active blogs. There are lots of tricks you can do that will give you highly active blogs. You could also look in blog directories although they aren't always that active. Postloop has a giant list of blogs in various niches which have lots of comments, although might not get that much traffic.

You can try search plugin for wordpress which allow ad dofollow links, example: inurl:wp-content/plugins/sem-dofollow

Although I already own Scrapebox and such, if all you want is to find are active blogs, then use the search methods that I mentioned above.

You can then save those searches by copying the url search string and save it in a document with a descriptive name as the hyperlink or you could just bookmark the search results page.

It's cheap and easy.

As many other warriors have suggested going to Google and typing in your keyword + blog will usually bring you a good amount of relevant high traffic blogs that you can comment on.

But, another highly effective way that I've found to discover high traffic blogs is by visiting forums in the niche that I am interested in.

I use a combination of Private proxies for the posting, public anonymous proxies for the searches, Scrapebox for finding the blogs and finally I use the exported list of valid blogs in GSA Search Engine Ranker. While these are all paid solutions, they are a minimal investment for the value they provide.

I hope this helps.

What if you get a list and do not like the blogs on it and feel frustrated because you HAVE to comment? Look for what you like and appreciate. I believe that you will, in due time, find as many blogs as you need and that you will also enjoy writing the comments.

I suggest using Google blog search and only commenting on new posts from the last 24h that's what gave me the best ROI!

I find forums are much better places to post on. So have some sort of forum posting campaign at the heart of your marketing strategy.