OK, I just looked at your site, and you already have a lot of galleries, including an off topic one, so you have some photographic interest. Build on it.
I think it is more interesting to start a photo thread in a regular forum, and then people can respond to a photo with another photo. Start one that says, "show us your...(dog, cat, house, whatever)" and see what happens.
We have also had several "Photo Challenge" threads, where someone will start out by asking for a photo of something, maybe a sign with a misspelled word, for example. The first person to come up with one issues the next challenge, etc.
You could also start a thread about what cameras or editing software people use.