Well, as .I'm sure most of us know teenagers are going to have sex regardless of if we don't want them too or not. Threatening them with consequence if you find out they are is only going to make them do it behind your back and possibly not be completely ready for it.
Parents should be teaching them about it.
Let your daughters know if they need to be on birth control you will take them, and encourage condom use as well.
Make sure your sons have condoms and drill it in their heads to use them.
I have heard some of my friends talking about their 15 year olds saying, "oh there's no way she's ready for that". "She's involved in too many activities, where would she have the time?" I say, "how old were you when you started having sex?" "when .I was a teenager .I participated in every possible activity in school and .I still found the time to do it".
Don't be blind