David Cameron has been criticised on Twitter after he joined the #BringBackOurGirls campaign calling for the rescue of the kidnapped Nigerian schoolgirls, with users asking whether he thinks this is “really the best he can do”.

Activists and celebrities including Sir Bob Geldof have previously called on Mr Cameron to send troops, intelligence agents and counter-terror personnel to Nigeria in a bid to speed up the process of finding the 276 girls who were snatched from their school in Chibok by the extremist group Boko Haram on 14 April.

Speaking today on the BBC’s Andrew Marr Show, the Prime Minister said that Britain “can’t just pile in and do whatever we like”, but did not rule out the prospect of troops being used if called upon in the future.

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At the end of the programme another guest, the CNN journalist Christiane Amanpour, offered Mr Cameron a sign with the words “#Bring Back Our Girls” written on it and asked if he wanted to “join the campaign”.

The social media slogan has been backed by the likes of US First Lady Michelle Obama, and calls for more to be done to free the missing schoolgirls.

Mr Cameron took the sign, saying he was “happy to do that” – and later tweeted that he was “proud to support #BringBackOurGirls”.

Now users on Twitter have been quick to point out that the point of an awareness campaign is “for people like us to get people like [Mr Cameron] to do something – not just join”.

One user, Jojo Moyes, said: “The #BringBackOurGirls hashtag is great. But it worries me that David Cameron thinks holding it up on TV is really the best he can do.”

Stig Abell said it was an example of “when the hashtag becomes the end itself”, while Stephanie Merritt wrote: “For the love of God, man, you could do a bit more than this.”

Explaining exactly what it is he was doing to help with the situation, Mr Cameron said he had agreed with the Nigerian president Goodluck Jonathan that Britain would “send out a team that includes some counter-terrorism and intelligence experts to work alongside the bigger American team that's going out there”.

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But he added: “We can't just pile in and do whatever we would like. It is immensely complicated because they are probably in this deep area of jungle that is three times the size of Wales, but it is good that efforts are being stepped up and we will do what we can.

“I think they are unlikely to ask for British troops but we have worked with the Nigerians in the past, in hostage rescue situations where British special forces have helped and advised, and so I said to President Jonathan, where we can help please ask and we'll see what we can do.”

Demonstrations in support of the missing Nigerian girls have been held around the world, while the social media campaign continues to grow.

Ms Obama and girls’ education campaigner Malala Yousafzai are among hundreds of people who have tweeted a photo of themselves with a sign reading #BringBackOurGirls in a show of support.

According to reports, the search is closing in on a forest near the border with Cameroon and the girls have been divided into at least four groups - which would make a rescue raid more difficult.

A spokesperson for the Foreign Office (FCO) said: “The scale and complexity of the incident and the environment means there are large information gaps.

“The priority for the team in the first instance is establishing the facts, such as the precise identities of those taken and what has actually happened, to help Nigeria build a better picture.”

The MoD has already linked up with the Nigerian armed forces, including the military which has operational control of the region where the kidnaps took place. There has been a meeting with the Americans to determine joint arrangements, areas of responsibility and what the next moves may be.

Metropolitan Police officers, which include the family liaison officers personally requested by Mr Jonathan, have met with Nigerian police to talk about how to tackle the huge demand for victim support.

Members of the UK team have also seen first-hand the pain and distress caused by the mass kidnapping in a meeting with a group representing the Chibok families, the FCO spokesman said.