The other option for building your portfolio is to check out your local studios and either book a few slots as models do studio days, or perhaps an event with multiple models. That way you can at least demonstrate your skills (within a model/studio environment)when seeking model on Tf basis....
As well as trawling modelling sites for nearby models and sending out notes to them, and often getting no response, try printing some cards with a few images on in styles you already do and have the courage to go up to likely looking models in the street and politely saying that you are a photographer looking to do a few new portraits to help improve your technique and portfolio. As long as you don't look too disreputable the worst they can do is dump them in the next bin.
I had some business cards made for me with each card showing an image of my work with my contact details including my website on the back (cards done by moo.com). Every time i'm out and i see someone who i think would be great to shoot i approach them, introduce myself and hand them my card. It is hard at first but you soon build confidence especially when they are willing to work with you.
I have business cards for my music photography which I hand out when folk ask about getting images at gigs. Might get another design made for fashion type work if I get more into it.
