Kathy had good advice for talking to neighbors, etc. When the people JUST left, its harder to find people as databases haven't been updated to show new addresses, numbers, etc.
Finding out who the lender is will not be any use to you. Until the bank owns the house, you will need the owners permission to speak to them.
Go to the Central Appraisal Distict website for the County the house is in. It will list the current owner and last known address (likely the house they just left).
Keep looking around the site for links to the County records and you should be able to do a search to find out what liens the house has filed for/against it (mortgage, etc.).
If you get to talk to the owners, simply tell them that you understand the house is vacant and neighbors indicated that they weren't coming back and you want to know if they are interested in selling. Its that simple with abandoned homeowners.
Two other tips:
1) Mail a letter to house they abandoned and write on the envelope
" return service requested" You will get the letter back and if they
left a forwarding order, the post office will list the new address on
the envelope.
2) Tape a note/letter in an envelope with the owners name on the outside
of it to the front door. Many times the owners have not gone far and
will go by the house to check mail, mow the grass, etc.