He quickly pulled down all his other social network profiles, leaving up the one that was posted as it was.
Is there anything else he could do to protect himself in this circumstance?
See sites like EncyclopediaDramatica.se (NSFW) for details why.
With that being said, abuse reports to network and hosting providers in first world countries usually are quite effective in these cases. If you can mitigate the exposure without ever communicating to the aggressors or stirring the pot, that's the way to go.
If it's a known 'shady' provider or someone not likely to care (Read: Voxility, Ecatel, Any ISP in mainland China, Most ISP's in NL/SE/IS) it's probably better not to send a report, as you'll just get it forwarded to the aggressor and show that their efforts are working to aggravate you.
Good luck, it's a tough situation to deal with.