Do you think my friend was wrong for taking my sisters virginity? ?

Your sister is searching for an excuse and someone to blame.   She is responsible for herself.  Your friend is not a friend and should be avoided.  In all of this, there is shifting of roles and responsibilities instead of good sense.  What is your parents opinion?

It's not about virginity but about the fact that he had sex (irrelevant of whether or not she's a virgin). She's 16, and if he's more than 2yrs older than her it is not legal. 

How can YOU feel betrayed? He didn't do anything to you.  

Nothing wrong with it. She would lose it anyway so! 

Love how some hypocrites get pissed and downvote me when they would support it if it was a boy with an older woman. 

Older men are always better for girls. 

If 16 is below the Age of Consent where you live, he is a rapist and your sister is not/will not be his only victim.  Your DUTY is to report him . . . . his fellow inmates will be the reward for his crime.

If he is 18 or older, he can be arrested. Let your parents call the police.  Or you can take care of him yourself, in your own way.