steepshot.io is the most popular Steem platform targeting photography. I think it tends to be lifestyle photography (like instagram) rather than photography blogs but it's worth checking out.
There are also lots of photography contests, for example:
#urban-photocontest tag
- 7 World鈥檚 Continents Photo Challenge by czechglobalhosts
- B&W Photo Contest by daveks
I'm sure you could combine your photography blogs into entries to these contests, or use contest entry posts to build an audience as a starting point!