An anonymous phone call is not enough evidence to take any form of legal action (temporary injunction, warrant, motion for return of personal property, or any form of lawsuit). I would first try to contact your neighbor to see if there is any basis in fact. It is possible that your neighbor will admit to the act. If that does not work, then try reporting it to animal control, the police, or sheriff's department. If that is not helpful, then a letter from an attorney may help or hiring a private investigator work.
This is not to be construed as legal advice. I do not have an attorney client relationship with you.
Why haven't you gone to the landowner and asked them about the rumor? If they refuse to speak with you call the police and/or animal control.
If we do not have a signed fee agreement I am not your attorney and this is not legal advice.