Someone want to mine with my bitcoin (www.elitecoinmine.com) Promises?
This is a scam.  Block all contact with this person and do not send any money, passwords, keys, or anything else.

Your friend is right, there is no such thing as mining "with" somebody's Bitcoin.  Mining requires specialized hardware (such as the AntMiner S9, which is a real device) but if one has that hardware, one doesn't need access to additional coins or anything else.

The scam will probably be organized in a way that it looks like you keep control of the coins throughout the process, and such that it is not obvious that your coins have been transferred to the scammer.  But in the end, when you try to get them back, you will find that you can't.