I created my wallet at blockchain.info
https://blockchain.info

  I get my wallet id ( for login) and I created my password too. After login I got my wallet address id to receive the funds (or public key for sharing)
as "1NXnzET4nk2Jkn6ySZfBZALV5eJyNJXBRk".  But  I am not finding any private key in that account.

Is I am missing something or these online wallet do not provide private keys to users ?