Have you heard of Guru Shots? I think I downloaded the app after seeing it featured in the app store awhile back, but I never really checked it out until my daughter told me how much she enjoys using it.
It looks like you can join in through their website or by downloading their app on your phone. I like that it doesn't just reward people who already have a big following somewhere else, everyone's photos are treated the same. Anyone can vote on the photos and that helps you get a feel for what others like about your pictures. You can even win prizes, but I'm not really in it for that purpose. I just think it's a cool concept.
Here's a short video to explain the premise.
If you enjoy photography, you might want to check it out!