Extortion Program has so far not affected the Mac OS to any great extent. It does not mean that it is not possible to create such malware. Eset has just discovered just such currently spreading online via bittorrent sites, disguised as a program for cracking expensive software like Adobe Premiere Pro CC and Microsoft Office 2016.
Eset call program OSX / Filecoder.E and writes that it is a amatösmässigt developed application written in the Swift. The developer has not taken the trouble to create a system to actually unlock the affected user's encrypted files, so even if you pay the ransom, you can kiss your files goodbye if you do not have a backup program does not come about.
installer you will be tricked to run has not signed with a developer certificate, so Mac OS default Gatekeeper (System Preferences -> Security & Privacy -> General) it may not run at all.
The only well-made the program appears to be the creation of encryption keys and the choice of crypto algorithm – it does not seem to be any weakness to exploit in order to recreate the files on the victim.
Eset has monitored the bitcoin-wallet as the creator of extortion program asked the victim to pay the ransom and have not seen any activity.