You can use whatever parental controls your Internet service provider offers and install any number of filtering devices but this always comes down to parents and kids agreeing on a set of rules regarding the computer.
What disturbs me most about your story is his exchanging personal information with people on the Internet. I am sure that he thinks that you are overreacting to possible dangers of this practice. There are pedophiles and other dangerous people who lurk on the Internet, in chat rooms, on porn sites, etc. They assume different identities and build up a relationship with kids that eventually leads to their asking the kids to meet them in person. Your son must NEVER give out any personal information about himself or any other member of your family. I'd suggest that he not be allowed to use the computer at all.
We can't prevent our kids from doing things we don't approve of outside our home but we can insist that they respect our family values within our home. Don't treat your son like he's always under suspicion of Internet abuse. The best that you can give him now is the beginning of an ongoing series of discussions about healthy sexual practices backed up by your family's values and beliefs. Although he may assume a know-it-all, non-responsive attitude toward your discussions with him, he needs to hear what you have to say and why you believe as you do.