When logged in to playhem, you can invite friends who aren't on playhem yet and you can build your list of friends from within the playhem community. 

To invite your friends who haven't yet joined in the playhem fun, click the image of the person with the '+' symbol on the bottom right of the playhem dashboard.

You'll see a neat pop-up that will allow you to invite friends via email or through facebook.

2. To add people to your list of friends within playhem, click on and expand the 'friends' list on the right side of the playhem dashboard:

With your friends list expanded, click 'find friends' and then click the 'sync with facebook' button. This will cross-reference your list of facebook friends against the entire playhem community and will invite all your facebook friends on playhem to be playhem friends. Also, you can manually search the playhem community to find a friend:

Alternatively, you can invite any player on the dashboard to be a playhem friend by hovering over their name / avatar (like you are going to challenge them) and simple clicking 'add as friend'.