yes they do but this is for people who have portfolios which I do not have.
No you don't have to have a portfolio to start up. Everyone starts somewhere. Even if you just have maybe some pictures of like family members or friends, you can use those to put up on your modelmayhem or onemodelplace profile. Just something to get yourself going. Once your account is all set up, you can start searching for models within your area who would be willing to shoot with you, you can either pay them or shoot tfp (trade for pictures)). For someone like you who doesn't have any current experience, it'd be best for you to pay a few models to shoot to get your portfolio moving. Once you have some actual models in your portfolio, you'll start reeling in tons of tfp shoots (hopefully). And if you get really, really good, some models might even pay you (there's lots of girls who aren't models, just average girls, who want a photographer who will shoot nude or lingerie photos of them to give to their boyfriends, in which case they might pay you).
Both modelmayhem and onemodelplace are free.