There are so many ways to promote your design blog niche. If you're still doing promotion to some specific design forums, there's nothing wrong to try general blog community for more campaign activity to your blog. A general blog community should always include design category or art category inside. Accordingly, there would be easier for the viewers to find your blog inside the community.
This article is updated, after almost a decade since it was published :D.
There were 8 once-new blog communities I mentioned in the initial post version, but only one that is still existing till now, which is Blog Engage!
Blog Engage is actually featuring general blog topics but they include 'Design' category for everyone who wants to submit their article there.
For more relevant content, you can visit a newer post from Webtoolhub.com entitled: 25 Top Websites to Submit Web Design Articles and News.
Blog Engage is also mentioned in the round up links there!
Do you know any other new general blog community that you are currently join on? Why don't you share with us why you like being part of it?