Help. A friend of mine has gotten involved with dangerous people and I think they underestimate them.?

Am I worrying too much? How can I show them the danger of the path they're on without being controlling or overbearing? They're fiercely independent and I don't know if they'd take me seriously. I really, really care about them as we've shared some of the most fun moments together, but these friends of hers are too much for me and the worry has started affecting my life in a drastic way. Do I let go? Inform her parents and other authorities? Christian answers would be much appreciated, though I will listen to any answer.