Does this person have an account on this Forum? If so you could make a post about them in the Reputation board. Or leave them negative trust.
How much does this person owe you? If it's a significant amount you could pursue legal action.
We probably need more information to help you better.
look at what he said :
hi
I am new here. recently a newbei give me work. I have done that work. after delivered work he does not pay me. I am trying to contact with him but he is offline.
what should I do now?
a newbie account gave him a work,after he finished it they didn't reply his message or email or whatever.
it's obvious,he's creating a new account to tell people to work for free.
so the only way is just to let it go.
learn from your mistakes and if you do some work again,ask them to use escrow to ensure it