You need to get in touch with PS customer service - they'll look up IP and the EI number of the PS machine to verify that it's being hacked. They'll ban the guy's account and machine that's hacking it.
Police authorities will do nothing except maybe make a report of it.
Also, your friend needs to secure his computers/accounts/and internet line.
EDIT: Here's the number from the
EULA
8. REPORTING ABUSE
To report violations of these Terms of Service call SCEA Consumer Services at 1-800-345-7669 or use the moderation tools that may be available on the Site where the conduct is occurring.