Am I right to worry about my sister?

My sister texts/talks to a lot of guys. She's only 16(I'm 17) and she basically has phone with them. So far she's been in 3 relationships that weren't good ones. They don't last very long either. There are a lot of her friends I don't like because they're very promiscuous or they drink/smoke. I don't want her to have a bad reputaton. As a slut or anything. And I certainly don't want her to continue sneaking out and lying to our mom. I just want to know if I'm being to overbearing by worrying about her since I know what she's doing.