I have a very small balance of bitcoin in c-cex online address, its a very small amount but it is showing up.
However, if I search the address in blockchain.info or blockexplorer.com, it says that the address has never been used, balance is zero.
Its been about 3 days already since that small amount of bitcoin was sent, shouldn't the balance have shown up on blockchain and blockexplorer by now?
The balance won't be sent out until you request a withdrawal to a specified address. Until then Cex records how much you have and has funds stored in its hot and cold wallets respectively. When you request a payment they will then send it from there - but there is no value in having your Bitcoin is a random address until then for them. Much easier to secure and maintain if you have less things to worry about.