I still don't understand how they stole your money.
You followed these steps:
1. You had your coins in an old wallet.
2. Scammers told you to sign a message, so you moved all your coins to a new wallet (which you control, right?)
So how they could steal your money? Try to be more clear...
Try to read it again properly,
he asked him to create a new wallet/address and send his coin to there.
afterwards they asked him to send his private key to 'sign the message' in order to get the airdrop
look at here :
They asked me to create a new wallet and send them the key to sign a message, damn i was so wrong
from my observation,it's not omisego fault because he get scammed by scammer.
it was not their official twitter if you look at it closely,
and it was not their first attempt to do it,you can find an imposter created the website to fool the airdropers.
like this one for example :
https://omisegotoken.comlesson : do not every give your keys to someone else no matter what,because they have an access to your money on it