The idea is looking good. Some thoughts for you:
1) Expect the standard chicken and egg problem - barbers (maybe you should call them hair stylists!) will not come in unless customers are there and customers will not come in till the right number of hair stylists are there
2) The app needs to be good, but the true value you will create here is the mass of users actively using it.
3) Creating value, most of the times, takes investment (not just ideas).
4) A pure online campaign, even if it goes viral, will bring in the potential users once but unless you have solved the catch 22 from point (1) above, they will just install and uninstall
5) You will have to start the basic user acquisition offline. Ideas on that:
a) Start local in your city
b) Get two guys on bikes to go shop to shop. Help them setup a sexy looking profile for their shop for free
c) Run a scheme for their customers where if they take a selfie after the haircut and upload it to the app as part of a review of the hair stylist then they join a lucky draw to win an iphone - initially might need to post a few boys/girls at the hair stylist's shop who look out for happy customers and pitch the idea to them.
Offcourse the huge valuation that you will get is when all this starts happening 'automatically' and scales through the sky....but realistically you will have to start the basic usage with something offline like above...