I know you said 'no parental advice' - but i can't resist a response to your observation - 'They're teenagers and trhat's what they do!'
Having raised three girls - the youngest of which is eighteen, I don;t agree that this behaviour is either excused or acceptable by virtue of age - as though it is some sort of rite of passage over which you have no control.
None of my girls helped themselves to things without asking because they were taught from a young age to respect the privacy and posessions of each other, and people around them.
That looks really sanctimonious in print, but the fact is, the family is a microcosm of the world outside. From whom else are your girls going to learn to respect others and their right to privaccy, if not from you.
By avoiding this issue, you are simply inferring that their behaviour is perfectly acceptable, a nuisance, but easily solved by simply side-stepping your responsibilities as a parent.
Sit your daughters down and have a chat about how they would feel if their posessions were pilfered in this way, and ask them to stop it. If they persist, then instigate a level of punishment until they accept that helping themselves is not going to continue.
It's a better solution for your daughters as maturing young adults, and for you, as the head of the family, and example for them to learn.