Sometimes on forums I see such messages as: "If you have any questions please, free to contact me!" or "If you need my help, you can ask me anytime". In such situations I want to be polite too and say not just "thank you", but something like "the same to you", "mutually", "likewise", "I wish the same to you". But I don't know which word to choose. Please tell me which word do you write in response to such messages? And what is more natural to say. Thanks in advance.
Long form: Thanks. Feel free to contact me as well if you have any questions.
Short form: Thanks. Same to you. (assuming the forum is an informal environment)
However, on many forums, you might want avoid such chit-chat since it's implied in the forum environment.