Question about the rules?

You can call the USGA and get a ruling that would be official.

The answer to your question lies in Rule 19

"If a ball in motion is accidently deflected or stopped by an outside agency, it is rub of the green, no penalty shall be incurred and it shall be played as it lies"

19/5 By another ball

"If a players ball in motion after a stroke is deflected or stopped by another ball in motion, the player shall play his ball as it lies"

The key phrases there are "rub of the green" and "play the ball as it lies". That means that if you can't find and identify the ball within the 5 minute rule allowed time period, the ball must be declared "lost" and you then have to put another ball into play under Rule 27. The exception to that is if there is reasonable evidence that the ball was actually deflected into a hazard and was "lost" in that hazard. In that case you apply Rule 25

In the situation you have stated you dont mention any hazard so you would have to go back to where you played the original ball from and if it was from the fairway drop another ball within 2 club lengths, no closer to the hole. If you hit it from the tee, then you can tee up anywhere in the teeing area.

In both Rule 27 situations you need to then add 1 penalty stroke

I hit his ball over onto another fairway

one stroke for hitting someone elses ball..

My Ball could not be found. What is the ruling?

one stroke for lost ball

Since he was not part of your group i dont think there is a penalty, but i'm not positive where you play your ball from, I think you would drop it where he hit it.

You drop your ball as close to the point as where is struck no penelty. As long as you know it was your ball before it became lost.

Lost ball, hit from previous location, add stroke. That's just dumb luck on that one, never heard that before.

i would say add a shot and drop another ball on the side (like what u do when it gets lost in trees or in water)

Time to buy a new ball.