my withheld Social seucity tax & Medicare tax not ted by my empl

My friend found this problem when he got the social security statement. His w-2 is good and shows everything but no any social security tax and medicare tax witheld for 2004 & 2005 are shown in the social security statement. Where is the money gone? Is it serious penalty for the employer if they dont the witheld tax to Social security office on purpose? please give some advice. Thanks a bunch!