If your EAD has expired, but you are still eligible to work, you are required to file for a renewal EAD by submitting a Form I-765, Application for Employment Authorization with the USCIS. It is important to remember that EAD cannot be renewed more than 120 days before your original EAD expires.
EAD Replacement
If you lost your EAD or it was stolen or mutilated, you have to apply for a replacement. If your EAD was issued with wrong information (misspelled name) because of an USCIS error, it can be replaced without paying the submission fee. Even to get a replacement, you have to file Form I-765 with the USCIS.
http://www.uscitizenship.info/us-visas/i-765-employment-authorization.jsp