N.H.
Well if you don't have the original in hand, go to the DMV or car tag website & there should be instructions on what to do & how to do it for lost title & I do know you're supposed to have the new owner sign a transfer of ownership paper, you can find that on the website too. You may be able to do a lot of what you need to, online but not sure of that. I believe you must have some sort of title in hand to sign it over but could be wrong on that also. Your best bet is to go to the website, here's the link: http://www.txdmv.gov/vehicles/titles/faq.htm
I'm sure if you have any questions on anything you're not sure of that you can call your local office for help (or any office may be able to answer questions). Hope that helps! Good luck.