Which crypto currency exchanges are using segwit (bc1) addresses for its users? Are any of the cryptocurrency exchanges using native segwit (bc1) addresses for any of its users?
As of November 2017, only Electrum wallet and blockchain.info are major services which support bech32 address format. A number of services use P2SH wrapped segwit scripts which is easier for backwards compatibility for the moment. This is expected due to the bech32 BIP (BIP 173) not being formalised at this point in time.