Hi. This could very well be a long post but I felt compelled to reply.
To try and get my point across I'm going to use my personal experience in this area as an example, so please bear with me. I'll try and keep it brief.
I accessed chat rooms and had similar discussions when I was about 10 or 11. I had fallen out with my friends and was lonely and lacking in self-confidence. At that age and when you're feeling vulnerable, those compliments are a BIG deal. Nothing much came of those chats and I don't remember speaking to the same people on a regular basis. Still, the conversations were highly inappropriate based on their nature and the fact that the people I was chatting to knew how old I was and made no effort to hide the fact they were adults. My parents never knew about any of this.
Anyway, fast forward a bit and I moved away (opposite end of the country) to a very remote community. My sister and I made friends with a large family (ranging in age from toddlers to mid twenties). I was 11 at the time. We all used to hang out in a big group, so the age gaps seemed irrelevant.
I only lived there for a short time, and then moved back close to where I used to live. I couldn't get a place at my local school so I was "home-schooled" for a term. As you can imagine, I was a bored 11 year old with no friends. When I left the remote community, I swapped numbers with the large family and we promised to stay in touch. One particular family member that I stayed in contact with was one of the oldest, a man in his early twenties.
It seems so inappropriate to me now, but at the time I thought nothing of the 100+ texts a day he used to send me. I have to get across that I was bored, lonely and isolated. My parents knew I talked to him, but they had no idea of the frequency/content of the texts. They have never known my passwords/ checked my phone. The biggest mistake was letting me have a phone in my bedroom at night with picture messaging capabilities. Enough said.
Inevitably, the shit hit the fan. I fell asleep with my phone open, next to me on the bed, and when my mum came into the room she went to move it and caught sight of the messages on the screen. Cue police interview etc etc, man duly caught and punished.
What sticks in my head about however was when my mum confronted me about this, my first words were, "It's not his fault. He didn't mean it. He's my friend." He had well and truly groomed me and although I have always been an intelligent person, at such a young age it never occurred to me that people may not be genuine.
What I'm trying to say through all of this is that you need to have a SERIOUS discussion with your daughter about WHY she feels the need to visit these sites and talk to these men. It is not normal behaviour for a happy 12 year old. So rather than concentrating all of your efforts on removing the problem, you need to tackle the CAUSE of the problem. She may be like me- lonely, shy, lacking in confidence and very, very good at hiding things. My parents didn't have a clue as I always had an excuse.
You are lucky in that you have caught this relatively early, it seems. She doesn't appear to have participated in anything that is likely to have a lasting effect on her.
She is also extremely lucky that she has been "found out" now, before the situation escalates and she finds herself in a similar situation to I did. Believe me, it was not pleasant. I'm 17 now, so 6 years on, and I find what happened still affects me in terms of how I view relationships and the like.
So if you take anything from my extremely long, rambly post, it is PLEASE talk to your daughter and find out why this is happening. If she won't talk to you then find someone she can talk to- family friend, teacher, counsellor etc. There's got to be a reason behind this.