In box 12D , my employer has listed how much THEY have contributed to my 401K this year , but no where do I see the amount that I have contributed. Any help?

[MayaD]

Employer matching contributions will not appear on your W-2. Only your contributions are reported in box 12 code D.  

[Opus 17]

Box 12, code D is elective deferrals -- it is the amount that you agreed to reduce your salary by, so that your employer would contribute it to the 401(k).  It does not include any free money from the employer (match or free contributions).

If your W-2 is wrong, you need to get a corrected W-2 from your employer.