you assume 'thanks' is informal. it is not. 'many thanks for your continued support' is no more formal than 'thank you for your continued support'. english speakers tend to speak more when they want to be more polite. the only place true grammatical formality exists is in our pronouns (thou, thee, ye).
Not true. Thanks is very much an informal world and it's not just because it's shorter. Not that I agree with your pronoun statement, but 'you' itself is a pronoun and by your logic if it's all about the pronoun then removing it from the sentence makes it less formal. 'Thanks' removes the 'you', therefore it's less formal.
We have a discussion here about the exclamative sentence "Thanks!" and not about the word "thanks". It is informal in English, i understand that. But in Romanian the informal "Mersi!" , imported from french is so obsolete and so unused that you should accept "Mulțumesc!" as a good translation !