One of the simplest and most effective ways to grow your email list and likewise your target list is to ask your biggest fans for their help! If they appreciate your email newsletter or email campaign, for whatever reasons, then these are the best people to ask for a referral.
And email marketing tools make this process simple. Highlight your forward-to-a-friend button in your next email campaign. Encourage sharing and be willing to share. Using an integrated sign-up request once the email is forwarded, someone you never would have reached otherwise is now able to sign up for your newsletter!
Those who do participate (and you know who they are through your email marketing tool) should be rewarded. A week later send a thank you note, better yet send a special offer or a valuable "How-To" document that has not yet been posted anywhere.
Email works well for new customer acquisition, it just needs to be executed properly and tactfully.