Spying

Hi I'm wanting to spy on my teenage daughters Facebook and Messenger. I trust her and I feel bad for doing it. But I don't trust the people who could be on it. I know I could just fix it so no one would be able to contact her without permission. But she can just change it or she could think it's some cute guy she's 16. Dose anyone know of an app that doesn't cost to use it.

Update: My daughter has been acting weird lately. She's been locking door when she talks on her phone. She cut her hair and has been lying about who she's hanging out with. I don't know what to do I'm losing her and I'm afraid it's going to get worse. She snuck out last night until 2 in the morning and I tried to ask her where she's been and told her it was a school night. She just went to her room and slammed the door.

Update: She is missing every since my last post. I tried doing what you all said and told her I'm here if she wanted to talk. I told her that she doesn't have to say anything if she doesn't want to. I told her I felt like I was loosing her and I wouldn't judge her for anything she's keeping secret. She said she meet a girl online that there in love. She said the girl has been giving her pills and she felt ashamed to tell me. I told her that it's fine and she can invite her over and will try to talk about everything she's confused about. She said that it would be really great she went to go pick her up. I haven't seen her since. They said they found her phone pulled apart and wiped down in her car. It was wiped down also and they found traces of her blood in the back seat. I can't believe I ignored my mother instinct and now my little girl is missing all because everyone said to trust a 16 year old and not break her trust she would probably be in her room right now just made at me In losing my mimd