You must boost this achievement with other players. There is no one playing this game online and a 4 player match without boosting is near impossible. I have played this game for a long time online with my friend and I have randomly joined a 4 player match 1 time in the 5 months I have had this game, unfortunately I lost the match and this is the only achievement I do not have on this game. I have only had a 3 player match spawn about 3 or 4 times during that period also, so a 4 player match is extremely rare to find legit.
Also, all 4 players must remain in the match until the end for the achievement to be unlocked.