He has been appointed chief executive of the anti-P Stellar Trust, which campaigns to raise awareness of the dangers of methamphetamine.
Mr Williams said he had seen how the drug affected his friend broadcaster Paul Holmes, the trust's official ambassador, whose stepdaughter Millie has been addicted to P for years.
"I've seen what that drug has done to his family. It has literally torn it apart," he told The Weekend Herald.
"I believe there's several hundred Millies out there. This issue is a huge social problem and we've got to do something about it."
He said he would be focusing on fundraising for the trust.
This involved approaching business owners with a vested interest in tackling the problem as most workplaces had employees with a P habit, which cost the company time and money.
