Yup, I also think more rural areas can be more risky for teenagers. The situation starball describes is exactly what happened to my DS: instead of drinking in pubs with older men to keep an eye on them, as 14-17 year-olds routinely did until a decade ago, they hang out in parks and car-parks, and occasionally in someone's home if their parents weren't around, without supervision, and drink/smoke/take whatever is offered to them.
Teenagers get into awful situations because dealers wait until they're drunk to offer them other drugs, and there are no adults around to keep the dealers away, or to say to the teenagers "You don't want that mate, it'll make you feel shit tomorrow and you'll owe him thirty quid you haven't got".
That kind of situation is happening every night, all round the country, in towns and cities as well as villages in the countryside... But urban areas offer more alternatives: more choice of friends and different social circles, cinemas and other things to do, pubs and clubs they might get into, part-time jobs they can't be stoned for...
But in most villages after dark, more kids are getting stoned than going to scouts, and that's all that is on offer to teenagers from lower income families. :(
I have in fact recently moved away from a village and into town, and a key reason was to get DS1 away from the group he'd got into... It has worked for us... I half-wish I'd done it a couple of years ago... Though realistically I think that if we'd moved when DS1 was at his worst, rather than this year when he was ready for change, I might have lost him completely.