The Home Office has spent £23,000 on Facebook advertisements warning Channel migrants that "we will return you" but ministers have been described as "naive" for thinking social media posts will deter crossings.
The campaign, which ran from December, also warned migrants not to "put your child's life in danger" by attempting to cross the Channel in small craft.
It was condemned by charities working in Calais, which accused the Home Office of "wasting money" on adverts unlikely to have any effect on "desperate people".
Clare Moseley, the founder of Care4Calais, said: "Refugees risk their lives to escape from some of the world's most dangerous countries, fully aware that this could be the last journey they make. It's extremely naive of this Government to think that social media ads will deter them. This isn't a choice."
A Freedom of Information request by the PA news agency found the Government had been paying to promote the adverts in languages including Kurdish, Arabic, Persian and Pashto.
One depicted migrants wearing lifejackets in a dinghy and warned: "Overcrowded boats are extremely dangerous. Even more so for children." Another showed sniffer dogs checking lorries, with the caption: "There is no hiding place."
Since the campaign launched, more than 9,250 migrants have crossed the Channel this year, surpassing last year's record total of 8,410. The crossings have continued despite attempts by the Home Office to stop them and make the route "unviable".
Migrants in France who had seen the Home Office ads online said they would make little difference in deterring them from attempting the crossing.
One 16-year-old boy from Afghanistan said: "I need to go to the UK. I am ready for anything to try and get there. I will try until I die."
A Sudanese man who saw the pictures on Facebook said: "We know that crossing and taking a boat is really dangerous, but we don't have the choice. The UK is our only chance, and better than Calais."
A 17-year-old boy living in northern France told PA: "It is not possible to stop us, we can't stop our journeys now. We have seen much worse than this and we have already put our lives at risk so nothing can stop us now."
The Home Office said its Facebook adverts had reached thousands of people, highlighting the risk to life of making the journeys.
Dan O'Mahoney, the clandestine Channel threat commander for the Home Office, said: "We are seeing an unacceptable rise in dangerous and unnecessary small boat crossings. The adverts are aimed at dissuading migrants in France and Belgium from making dangerous attempts to enter the UK."