iPhone 6+, Find my iPhone in lost mode
Based on this article from Apple:


  Turn off Lost Mode or change your contact info
  
  You can turn off Lost Mode by entering the passcode on the device, or by following the steps below. You can also follow the steps below to change the contact information displayed on your lost device.
  
  Note:   If your credit and debit cards for Apple Pay were suspended
  because you put your iPhone 6 or iPhone 6 Plus in Lost Mode, when you
  turn off Lost Mode and sign back in to iCloud, you can resume using
  your cards.
  
  
  Go to Find My iPhone on iCloud.com.
  
  
  If you don’t see Find My iPhone on iCloud.com, your account just has
  access to iCloud web-only features. To gain access to other iCloud
  features, set up iCloud on your iOS device or Mac.
  
  
  Click All Devices, then select the device that’s in Lost Mode.
  Click Lost Mode, then change the information or click Stop Lost Mode.
  


So if the person who picked up your phone is able to unlock your phone (using the correct passcode), they can disable Lost Mode. However, they won't be able to use your credit card information unless they also know your iCloud password.