The only way for you to lock or wipe the phone is if it can still be found.
You can sign in to the following site to see if the device is still registered with the service.https://www.icloud.com/#find
If your iPhone is registered there and the person who has it now has not removed it from the network, you can send it messages, track it's location and remotely wipe your personal data off the drive.
If you are running iOS 6 or later you will also have access to Lost mode. While in Lost mode, your device will keep track of where it’s been and report back to you any time you check in with the Find My iPhone app.
Whether it can be found or not, your next step is to suspend data service so that others can not use the phone. You would need to contact your cellular provider for this.
Note: Due to security reasons, I can not do any of this for you. It is between you and the phone company.
Hopefully, this info will answer your question and if so please don't forget to rate my service
. If you continue to have questions on this topic, do not rate yet, just reply back to this discussion
. I will be more than happy to work with you further.
Thanks and good luck,