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.
Here are 8 new blog communities for you to start with:
1. Blog Competition
BlogCompetition is a digg like competition, win upto $2500, with monthly prizes, and a weekly featured article.
Members can vote to various posts which are submitted under certain category.
Blog Competition is powered by: Pligg
Paid listings are done as you would any other auction except that it is used for advertising, sponsored reviews and paid guest posting.
Simply find an opportunity you like and make a bid.
Promote yourself by doing and giving interviews. Gain interview content and spread your message. You will have a chance to meet another great bloggers and sending direct invitation to do interview at Peopleized
4. Dot Dash Create
Personally, I love this community because one of the features could be useful to accommodate what designers need to promote their skill. Dot Dash Create have a cool feature that allows you to list recent project that you've currently working on, which is very good service to promote your design portfolio online in a community.