If you are trying to access your W-2 online, you can contact your company's payroll department to help you. If that is unsuccessful, you can request they mail a paper copy to your new address. The IRS will also assist you, but they prefer you to wait until the end of February. At that time, you can contact the IRS Taxpayer Assistance Center here: Taxpayer Assistance Center Office Locator
Here is an article with more information: What To Do If You Haven't Received a W-2