Find my Friends displaying email addresses, not contact portraits or names
I suffered from the email-address-instead-of-name problem after replacing my phone's local contact info with a sync copy from my gmail account. this seemed to work for me (ios7):


click on the contact name in the 'find my friends' window 
click the 'contact' button at top left
click 'add to existing contact'
select the relevant person in your contacts list; this will seem to add a duplicate email address, and you might want to clean that up later


restart Find My Friends... is now showing names (for me at least)... good luck.