I think very few if any use it but...
Using entity linked lists / entity arrays plugin (eLL) I might find pos of player 5 like this:
Code:

---

entity* ent0;
define _id, skill38;

// create players
function plfCreate() {
	var i = 0;
	eLLsDelete();
	eLLsNew(1);
	while(i < 10) {
		ent0 = ent_create(<player.mdl>, pos, function);
		ent0._id = i + 1;
		eLLPush(0, ent0);
		i += 1;
	}
}

// find player pos
function plfPosFind(id, &_pos) {
	eLLNextReset(0);
	ent0 = eLLNext(0);
	while(ent0 != NULL) {
		if (ent0._id == id) {
			vec_set(_pos, ent0.x);
			return(1);
		}
		ent0 = eLLNext(0);
	}
	return(0);
}

//  plfPosFind(5, temp);

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get eLL here (ver. 6.5 will be uploaded later)