'Youth' (or 'yoof') as a collective noun (youth club, youth culture) clearly hasn't any ethnic connotations. But as applied to an individual person - a youth/yoof, youths/yoofs?
I first came across that usage in fairy stories as a child - youths and maidens - and always assumed it was archaic or at least old-fashioned or provincial ; I remember thinking it odd when my South Yorkshire born grandfather said, 'When I was a youth...' If I am right about that, why has the word come back into everyday usage?
Nowadays it always seems to me to have a slightly pejorative tone - would you refer to your favourite nephew as a 'youth' or to the Scouts doing a wonderful job helping old people as 'youths'? 'Youths' or 'yoofs' implies to me 'getting up to no good' And it also implies to me - perhaps wrongly, in the light of what Rachael and Mr_Numbers say - that it is probably being applied to young people (a better term, in my view) who are, at any rate mainly, black.