There are tons of companies big and small that do this.

Run it yourself through a contest app
Facebook promotions through companies like offer pop
This is the company that is runnings Starbucks coffee for life promotion

They key thing is not necessarily running a giveaway but finding the right giveaway to attract your target audience. The only bad thing is you do get a chunk of people that are only in it for the promotion so overtime you need to weed out those contest players.