How can a new fashion designer launch his line if not known in the market?

Fashion is a very closely knitted community. So in order to get your name out there it is very important to create a real personal network, getting to know people of the business. This can be done through attending fashion shows and exhibitions and other social events. In this industry word of mouth matters a lot. 

Also, internet has provided a great medium to promote any new product specially in the untested waters. But for that a solid social media strategy with the right content mix is very vital along with the right product. 

In my opinion, starting a website alone to launch your new line will help. Or you can also consider starting to advertise it in the best growing social media - Facebook. Surprisingly it helps to reach all kinds of people, regardless of age.