I just started a curated newsletter about personal finance for millennials. Each issue includes 10 curated articles from various sources about investing, budgeting, paying off loans, and etc. I do not have any subscribers yet.
1. Have a sweepstakes/giveaway (product specific to the audience you want). It will be slow from the start but once you start posting winners from your giveaway it will set the ball into motion and create a network effect with everyone sharing the event (use facebook or google connect for one click registration to your sweepstakes)
2. Have an event. allow users who signup via email to your event to come for free.