There are 2 conversations going on in this thread.
1 group of people is talking about being the first one to raise the pot for a "standard" 3x the BB. This is not a 3bet, but just a raise.
The other group is talking about re-raising somebody who already raised.
^^This^^ is actually a 3bet. Also known as Re-Raise.
YOU CANNOT 3 BET LIMPERS!!!! because you cannot "re-raise" when nobody has raised. So all these replies that advocate "limping along" instead of 3betting have their terminology confused.
Anyways....there are solutions to both dilemmas; whichever conversation you are having in this thread. Which basically come down to either "don't raise" or "raise more"
Any bets and raises you make should have a purpose. If the purpose of your raise is to thin the field, but then your raise NEVER accomplishes that goal then your raise is pointless. Either call along, or fold, or raise bigger but don't just keep doing the same thing and then wonder "why don't my raises ever work?"
Here is an example of the most pointless raise: 4 or 5 players limp and then the BB min raises. What on earth could possibly be the point of that raise? (I actually see that all the time). If you have a big hand, raise big. If you have a speculative hand, check your option and take a free flop. The min raise only builds a pot when you're out of position. Nobody who limped will fold to this raise as their hand is still the same, but now their
pot odds are even better. If you have AA it is stupid. If you have 22 it is stupid. if you have AK it is stupid. if you have 78s it it stupid. There is literally not a single hand I can imagine where min raising a bunch of limpers serves any purpose whatsoever.
So....in short. Have a purpose for any raise you make. Are you
bluffing? Are you value betting? Are you thinning the field? Are you isolating a weak player in position? Define your goal, and then develop a plan from there. Until you know what you are trying to achieve it's hard to evaluate your success....