networksetup -connectpppoeservice "VPN" does not work anymore on Yosemite
I had the some problem and a working solution like this:

Before Yosemite

networksetup -connectpppoeservice 'MY-VPN-SERVICE-NAME'


On Yosemite

scutil --nc start 'MY-VPN-SERVICE-NAME'


I found the hint on Robert's Blog http://roosbertl.blogspot.de/2014/10/auto-connect-osx-yosemite-ipsec-vpn-on.html

Works für IPSec and PPTP