I am 40, male, with three kids Boy-13, Boy-10, Girl-5.
And I know I may still be in the optimistic younger-teen years of our oldest, and he is a great kid, but I have to say: NO, I don't generally support a parent drug testing their teen, because of the following reason:
1) A parent should have a pretty good handle on his or her teens comings and goings, their friends, the amount of money they have and spend, and what they do with their time.
2) A parent should have a close relationship with their teen so that they can discuss drug use, and drug temptation
3) A parent should be able to tell if there teen child is acting strangely or not themselves, and find out what the problems are; it may not always be drugs, but the warning signs are usually there if you watch for them.
So, *IF* a parent is doing all of the above, then a drug test won't normally be needed, IMHO, because you the parent should be able to tell if their child is on drugs, at least with some level of certainty.
Therefore, you could say that I see "drug testing of teens" as a LAST RESORT, when communication has broken down, trust is gone, and you just "have to know" so that you can FORCE your child to TAKE the help you can provide for them. If you get to that point, the drug taking (if factual) is probably a symptom of a larger problem in the teen and the families' life.
TJR