Learn English – Is “haven’t met the friend” correct in British English

Though grammatically valid and understandable, this sounds a bit like something you might read on a greeting card. It's a bit formal, and beginning the sentence with "Wishing you" instead of "I'm wishing you" or "We're wishing you" adds the implied subject and sounds a bit unnatural for speech.

If you're sending them a card or an email or something, this could sound perfectly fine:

Wishing you the very best of luck with your presentation!

Sincerely,

Your Name

That sounds natural in that context. If you're speaking to them in person, though, it sounds a bit odd. "The very best of luck" sounds oddly formal, and as I mentioned before you're removing the subject from the sentence, which isn't how people normally speak. If you're talking to them in person, you might say:

I (we) wish you the best of luck with your presentation!

Still a bit formal, but adding the subject makes it more natural in speech. More natural-sounding would be:

Best of luck with your presentation!

Or most commonly said:

Good luck with your presentation!

When you are referring to duration, use “for” or “in”; when referring to the last time something happened, use “since”. “Since” will always require that you specify a point in time, not a span.

Your second option is grammatical and perhaps even ideal in BrE. For AmE, if you haven't rendezvoused, visited, or met up with your friend in a year, I recommend you say:

I haven't seen my friend for a year.

It all depends on exactly what you wish to convey, but some people may associate “meeting” with either the impossible-to-repeat act of making someone's acquaintance or the cold sense of business meetings.