To my ears and eyes, it´s a first. Never had seen it before.
If you have the fixed expression TIA and a shining-brand-new (even exotic) "thanks already" which one are you going to choose? I am writting a book (of short stories...) and I preffer the latter to the former.
Thus, if there are both as words (sentences) of choice, I am picking TIA.
Anyway, if you post a message and say thanks, you are already showing gratitude in advance, aren´t you?
This way, you don´t need to post another one, just to say thanks. See?
Now, some interesting stuff: =>
"Neither is correct and both come across as presumptive and rude in business correspondence. By thanking someone in advance, you're essentially saying, "I really need your help, but I'm not willing to take the time to thank you properly after you've helped me". Why not just say, "I appreciate any assistance you can offer", then after they have helped you, say thanks the traditional way?"
"here are courteous alternatives to consider:
"Thank you for considering my request." (Just by reading to the end of your message, your reader has considered your request.)
"I will be grateful for any help you can provide."
"I will appreciate your help with this situation."
"I hope you will be able to provide the information."
You can also sound polite by simply omitting the "in advance":
"Thank you for any help you can provide." (But be sure to thank the individual after you receive the help too.)
I began with the example "Thank you in advance for your attention to this matter." That sentence has two offending phrases. The second one is "for your attention to this matter." That bureaucratic expression has appeared in billions of letters, especially ones asking for late payments. It's so tired after being spit out of typewriters and computers for decades. Give it a rest. Replace it with something more specific that fits your situation.
Thank you in advance for avoiding the above phrases.