I definitely wouldn't go off a single person that I didn't know personally's Tweets, usually on anything of consequence you would look for multiple confirmations on Twitter and some evidence of the event in other places online.
Id say call the school, another parent, or any other point of contact you could possible imagine before you go smashing up your car in a panic... I never really understood the lapse of social responsibility in these situations. Not to take away from the complete horror at the thought of your child being shot or kidnapped (I could never come close to knowing how that feels) but these are the inherent dangers that come with new technologies (specifically information tech). I mean really though, what are these parents going to do to protect their kids against armed gunmen? We have witnessed the powerful benefit of twitter and FB, etc in assisting communities and families in the aftermath of disaster, but what have these "instant info systems" done to help people mid disaster or to prevent one all together? It's fast, but its not time travel... Id say just keep your reliable sources on check and close at hand. But then again, I cant say I wouldn't go barreling down the street in a panic to make sure my loved one were ok.
Being a movie superhero I'd jump in the car and race down there, leaping into the fray and killing all the terrorists, including the midget pretending to be the cute little girl. Then I'd get a medal, and a pony.
You though, lacking superpowers, couldn't help if you were there. So I dunno, maybe you should frantically search until you get positive evidence, and an idea of what you could do to help, before you decide what to do.
There are laws to deal with the guy if these was a scheme to profit. If he was deluded there's no reason to take actions, he's no worse than the idiots who ran around because of his rumors. In fact his action was better. By forwarding his news he's inviting conversation and investigation, by running off to the school the terrified parents are actually potentially causing a problem.
