Hi, is it okay to use ethereum address to sign a message? because I don't have my private key of my bitcoin address.
I believe they have been accepted before. Just make sure that is the oldest of the addresses that you can sign, and message cyrus/theymos every now, and then, and be prepared to wait for a few months. A few users seem to have been just waiting under a year. So you could be waiting a long time for it to be recovered.
And you`ll have to wait, maybe for months regardless of type of adress, that you are giving. Apparently, there is a great amount of accounts that need restoring. 