You need to report all your income or else there will be penalties & interest assessed by the IRS. Since your employer has already send a copy of your W-2 to the IRS, when you file your return, there will be a mismatch of data which can lead to interest and penalties.
There are multiple options here:
1) Contact the IRS. Please visit IRS - W2 Information on steps to contact the IRS.
2) If the IRS is unable to help, then you will need to Fill out Form 4852, which is a substitute for Form W-2 if you have not received it. You can fill this form in TurboTax. However, the IRS doesn't allow Form 4852 to be filed electronically, so you will need to mail it to the IRS.
3) You can file an extension to give you extra time to receive your W-2. Please visit File Extension to get started on filing the extension through TurboTax. Keep in mind that you still need to pay any taxes due by the tax deadline, so an extension to file is not an extension of time to pay any taxes you may owe. So if there is any taxes due, you will still need to pay them before the filing deadline or the IRS will add interest and penalties.
Please visit What To Do If You Haven't Received a W-2 for more information.
