Use the Launch Effect Theme
Launch Effect is a free theme that allows you to pretty quickly get a theme up with an email capture. Each person that enters their email is given a unique trackable link to share (which you can set rewards for). All the tracking is done in your Wordpress back-end. It works pretty slick. There is a premium theme that you can pay for if you want extra features. There are some other options, but this is the best. You can potentially use a "Coming Soon" plugin or theme, but that requires some unnecessary hacking.