If the property is not currently for sale but you want to know who owns it to make an offer, first go to your townships' tax assessors office. Find your house on the tax maps then ask about the property next door , get the lot and block number and then find out who the owner is. The tax assessor has all the current information for you. Then ask a local realtor to do a market analysis on the value and consult a real estate attorney on the proper way to offer to purchase the property.
If its already listed and you want to purchase it, ask a local realtor to find it in the MLS and ask him/her to do an evaluation of the market value and have him/her help you write a contract to purchase.