The hashtag began to trend yesterday.
It was a response to the Israeli operations that began on 8 July.
At least 159 Palestinians have died since Operation Protective Edge began, according to Gaza officials.
Israel says that it is targeting Hamas, but the UN has estimated that 77% of the people killed in Gaza have been civilians.
CNN correspondent Jake Tapper was among a number of social media users who noted that Hitler was no friend of the Arabs.
And a huge number of pro-Palestinians were critical of the hashtag.
The UN Security Council called for a ceasefire and peace talks on Saturday.
The IDF says it has so far struck some 1,320 "terror" sites across Gaza, while Hamas have launched more than 800 rockets at Israel.