Talk to a few people that you would hope would be ideal users of your app -- ask them about their habits and media they consume to better identify potential channels that you could use to reach similar people.

Your earliest users are most likely to be ones who are already doing activities with regards to fashion -- perhaps check out /r/malefashionadvice on reddit and search for other online interest communities. I would bet there are instagram, pinterest and twitter communities around fashion.

Measure the success of your campaigns across channels, and the retention of users across each. You should decide if you plan to grow users by being 'viral' (fast growth, but user's don't stay long) or 'sticky' (slower growth, longer usage).

Any users you get and keep are likely to be the best advocates and already know similar users, so empower/incentivize them to invite the friends they think would be interested -- ideally in some way that is natural to the product. In the ideal case, the product is so good, they will immediately want to tell their friends who would be interested.

Finding an effective and repeatable marketing strategy can require as much thought and effort as the product itself.