More Guidance. Talk to your child, seek professional help and above all, try to help control the web access by using parental controls and the like.But child education is probably the most important.
Supervision. I don't know your child's age, but none the less, i wonder how much your kid is supervised while online? A conversation needs to take place, on going in fact, with your child and with respect to all of his or her activities, not just the internet. You need to project an attitude of unconditional acceptance toward your kid's communication with you, so he or she is comfortable approaching you.