I am not a fan of internet social sites because professional photographers and agencies are not scouting talent on the web,-they are just too busy booking their models and shooting professional jobs- it is just truly a waste of time.
Also you want quality and much that is out there on the web is truly amateur. In my memoir Almost 5'4" I do confront my own mistakes with the web and I hope my mistakes on the web can inspire you of what NOT to do. I think the book is also a warning for girls about the misconceptions of the Internet.
To be a model, I would get a compcard, mail it to agencies and strive to work with a professional photographer. You won't find a professional on the web. The more you strive to get professional photos the better for your pursuits. Then get a compcard and mail, mail, mail, mail, it to agencies. The best way to start modeling is NOT on the internet.