1.) Start with a direct approach. If the owner is living on the property, you can approach the owner and voice your concerns in a calm manner. If the owner does not live on the property, try your best to make contact with the person over the phone about the issue.
2.) Ensure that the person really is the property owner. If the person on the property is actually just a tenant, you have another step before going to authorities. Find out who is renting out the property and contact that person. You can do this through your county's property tax assessor's office. Once you have this information, send a letter to the landlord, including pictures of the negligence for added effect.
3.) Complain to the lender of the property if it is in a foreclosed state. Do not settle for a customer service representative on this one. Make sure you speak with management, and go all the way up to the chief executive officer if that is what it takes. If this isn't giving you fast enough results, go to your state's governmental website and find the state mortgage regulator. Contact the regulator.
4.) Contact your local government officials. Find the number for your local public health department and call the office to explain what is going on. Make sure to take note of all sanitation and safety issues involving the property.
5.) If you must contact a lawyer, a real estate attorney would be best. You may be able to sue the owner of the property. Remember that these cases can drag on and be expensive, so this step should only be used as a last resort.