Think of any good ones? I know we have both been on the big D. Probably have not posted there in ten years or so. I went by "Fractality." Last time I looked I no longer existed.
I actually haven't gotten much good feedback there, or really gotten noticed at all. Too many wannabe artistic types, substantive critique is a valued commodity and getting it requires too much networking and very frequent participation in their communities.
I really think a site like this where people know you and are happy to have a conversation is a better bet. If you have a thick enough skin to take bullshit too.
I just mentioned that site because it is the "biggest" free place. As I noted I was done with it as well. For a new artist trying to find ones way, any response can be helpful. Just how helpful may depend upon many things and especially, as you bring up, the thickness of ones skin.
Sorry, I really have no options for this question. All the typical choices seem too obvious to mention; Facebook, Instagram, Pinterest, Etsy, ad infinitum.
Not much first hand to share with that world.