Settings>Applications>All and find the stock text message app. Once found, disable it. Your third party text message app will now become the default app and appear on your lock screen.
I found out that disabling the stock would not allow me to receive mms messages.
Go sms newest update has it its basic settings a way to make it your preferred sms app and it will make it show on your lock screen. Please enable the stock messaging app and just turn off its notifications.