[Obviously, I am not your lawyer, let alone a lawyer at all just yet, and this is just an idle brainstorm, not legal advice.]
Anyway, to me, there are two preliminary issues:
1) Are the interns agents of n+1?
Principals (e.g. employers) are vicariously liable for the torts of their agents (e.g. employees), as long as the tort was committed during and in the scope of the agency. Conceivably, if you were sued, you could argue that n+1 can’t be liable for the interns’ torts, because either a) they’re not your agents, or b) the personals stuff wasn’t in the scope of their agency. The fact that you don’t pay the interns is the best/only thing you have going for you here, though, and given how intertwined n+1 is with this personals site, the no-agent argument probably wouldn’t fly.
2) Is Section 230 relevant?
You know all about the CDA. If the interns are more-or-less passive conduits, giving these ads titles and posting them on Tumblr, they/you can’t be treated as the speaker of the info, and thus you’re safe from any claim based on the content of the ad itself. But this isn’t what you’re interested in.
Rather, the idea is that someone gets sexually assaulted on one of these sad young literary dates, right? In that case, the victim would most likely sue you on a simple common-law negligence theory, claiming that in some way (e.g. failing to screen) n+1 breached the standard of due care that any person/entity owes to the people its actions would foreseeably affect.
Now, negligence cases are notoriously fact- and jury-dependent. And to find any settled principles of law for cases like this would require at least a couple hours researching relevant state cases (which, even if I felt like doing, would require access to databases I no longer have). I did, however, just read about a case in which a woman in California sued Match.com after a “match” with a history of sexual offenses sexually assaulted her on a date. According to the really poorly drafted complaint, the claim was based on a California consumer protection statute that appears to basically incorporate a negligence standard into the state code. As a result of the lawsuit, Match.com announced a policy where they’d check members against a sex offenders registry, and the case promptly settled. Who knows what would’ve happened in court.
So, what to do? I think a relevant analogy here is to premise liability cases, where somebody gets hurt because of some condition on somebody else’s property (like a loose cabinet) and then sues the owner on a negligence theory. A lot of states have byzantine distinctions to determine what duty the owner owed (New York doesn’t anymore), but the bottom line across the board is that the owner could have avoided liability if he’d fixed the problem or clearly warned about it. Along those lines, it would definitely not hurt to add a caveat dater making clear that you don’t do any sort of background checks on these folks and so on.
What a surprise, a bunch of legal ink spilled for a common-sense conclusion!