They still make money off the website. If they want to vet only the jobs ads, then that is all they should have on their site.
Care to address the Yahoo email scenario then? Can I sue Yahoo if I fall for a Nigerian 419 scam? Could I sue Microsoft if the scam was typed up in Word? Can I sue the manufacturer of my computer? The inventor of the Internet?
What you are proposing is offensive to the concept of justice. A person should not be held liable for something that was done without their permission and without their knowledge. If the principle that you insist on here were to be applied, there would be no limit to liability anywhere, anytime, and the entire country would grind to a halt under the weight of an endless flood of lawsuits.