You can set up email subscriptions here > Appearance > Widgets > Follow Blog Widgets by using this guide > http://en.support.wordpress.com/widgets/follow-blog-widget/
If you would like a follow button to appear on the bottom right hand corner of your site for those who do not have WordPress.com accounts go to > Settings > Reading and scroll down to Follower Settings:
These settings change emails sent from your blog to followers.
Logged out users __ Show follow button to logged out users.
Checking this will present a follow button to logged out users in the bottom corner of their screen.
Find Friends Who Use WordPress > http://en.blog.wordpress.com/2012/05/01/find-friends/
You can customize the contact form with multiple fields, change the email address where you'll be notified, and mark feedbacks as spam from your dashboard. http://en.support.wordpress.com/contact-form/
See also Inviting Contributors, Followers, and Viewers http://en.support.wordpress.com/adding-users/
Note: As a spammer prevention you are limited to sending out 10 invitations at one point in time. Then wait and send out 10 more.