The best way to get the most appropriate advice for the situation is to provide a little more detail about the transaction, as without knowing a few key facts, it's hard to know the best way to help and there could be any number of factors that change what approach to take in a situation like this. (Also best to leave names out of it - they will be deleted by a moderator sooner or later, anyway).
The most important questions - when did you purchase the item? How did you pay? Where is the seller located and what was / is the estimated arrival date of the purchase? Or, have you already received the item but it's not as described? And lastly, can you clarify what you mean by offline? Has the seller disappeared completely (suggesting that their account is deregistered), or have they gone on holidays? Also, have they responded to any messages you've sent so far?
