You could say "no problem" (an informal "you're welcome") and then say "me too"

"Ditto" is quite informal among friends and/or co-workers whom you know. For example, if you are with a friend and he or she says I really like that (text, movie, book, information, car, and so forth) you simply reply "ditto." Remember, "ditto" is a very informal English term but not uncommon in day-to-day usage. Other informal terms: "likewise", "same here", "I agree."

"I agree, thank you" or perhaps "Thanks from me too" or "I found it useful too, thanks."

An informal and polite way to put it would be, "Totally", which would be implied as short for, "I totally agree with you".