Stolen Social Security Card?

When you cant find your social security after a few hours of searching, i guess its safe to assume that it got stolen. now im confused. when someone has your card, they have the number. but when you report a stolen/lost card, all you have to do is apply for a new one, and you get one with the exact same numbers...doesn't that defeat the purpose of reporting a stolen card? i guess what im trying to say is this, how can you protect your identity (even after receiving a new card). when there is still someone out there with YOUR card?