[Misiur]

Your code is good. All I would improve, would be getting the NPC/Zombie position once, not on every iteration.

pawn Code:

new ids[MAX_PLAYERS], count = 0; 
new Float:x, Float:y, Float:z; 
FCNPC_GetPosition(npcid, x, y, z); 

for(new playerid = 0; playerid < MAX_PLAYERS; playerid++) 
{
    if(!IsPlayerNPC(playerid) && IsPlayerConnected(playerid)) 
    {
        if(IsPlayerInRangeOfPoint(playerid, GetVictimDetectRange[playerid], x, y, z) && GetPlayerState(playerid) == PLAYER_STATE_ONFOOT && GetPlayerInterior(playerid) == 0 && GetPlayerVirtualWorld(playerid) == 0) 
        {
            ids[count] = playerid; 
            count++; 
        }
    } 
} 
if(count != 0) 
{ 
    return ids[random(count)]; 
} 

return INVALID_PLAYER_ID;

Other problem you might run into is how often you run this, it might make the zombie twitch between each player