Go to http://www.taxnetusa.com. It will let you search property tax records for the state of Texas. It will show who owns the property. It will give an address, but won't give a phone number. I'm assuming you're talking about a vacant lot. You might have to look someone up in the white pages.
Go to the town office with the street address or the map and lot #. The town will have a map so you can find the map and lot # if you know where it is. From there you just ask who the tax bill goes to and write a letter.