Golf Rules / Where to hit ???

In a social game, player A hit a shot and it landed toward some trees on the right. From where they are standing on the fairway, they could see a buggy drives toward to where his ball was last seen.

Player A later reached the spot where he hit his ball but he couldn't find it !!! Player A thinks a golfer from another group may have pick up his ball !

He notifies Player B, C and D. He played two balls, one from the spot of the 1st lost ball and another from the previous spot.

Will player A be penalized for playing 2 balls or wrong proceeding ?

his ball was seen...and later missing...so there r doubts...

Rule 3-3:

3-3. Doubt as to Procedure
a. Procedure
In stroke play, if a competitor is doubtful of his rights or the correct
procedure during the play of a hole, he may, without penalty, complete
the hole with two balls.
After the doubtful situation has arisen and before taking further action,
the competitor must announce to his marker or fellow-competitor that
he intends to play two balls and which ball he wishes to count if the
Rules permit.

The competitor must report the facts of the situation to the Committee
before returning his score card. If he fails to do so, he is disqualified.
....

The ball was taken by the other golfer from another buggy was on assumption, not virtually certain, therefore A has to treat as lost ball and play from last position.

If in doubt, it is ok to play with 2 balls and later consult committee.

If match play, no such thing as playing 2 balls.

But since ah Lau says social game, I suppose play from previous position and treat 1st shot as lost ball should be the way to go. T&Cs for the lost ball applies. I.e. Stroke + distance