If the things he says are illegal, then you can report them to the appropriate authorities.
There is a difference between his private life and his life as a company employee. In his private life he can do what he wants as long as it is legal, even if it is offensive. (I can't judge whether he has done anything illegal, you might post on law.stackexchange.com with details).
When he writes things about you, a co-worker, then it is not his private life. It's the company's business. They are responsible for you being kept free them harrassment, including sexual harassment, and for you being kept free from hostility towards you - as far as it is part of your work, and coworkers posting things on the internet about you on their private website is part of your work.
If this is reported to HR, including evidence (which you easily get by printing out his website), then they would have to act promptly. It doesn't really matter who reports it, but they might need your statement to determine that this is actually harassment. If I reported it, I wouldn't know for sure whether what I see isn't some weird thing between boyfriend and girlfriend. You would have to say that this is indeed offensive to you.
Things are worse for the offender if the website is an any way linked to your employer. If the average reader would think "I wouldn't want to do business with the company employing this freak", then consequences for him are guaranteed.