I got my H1B in October but I did not get it stamped yet. My employer did not hold my social security and Medicare taxes nor I received and social security wages.

How do I tackle this situation. Do I have to pay social security and medicare taxes from my own pocket (eventhough I did not receive any benefits). Do I have to fill any extra tax forms.

I greatly appreciate a reply for this question. Thanks a ton in advance.

It is your employer's problem. If in future, they want you to pay back your share of FICA taxes, you must pay it.