Hampshire Police have obtained a European arrest warrant for the parents, Brett and Naghmeh King, on the issue of 'neglect'.
Two Civil Guard guards have been stationed outside a luxury apartment in the resort of Estepona after Hampshire Police received a number of 'positive sightings' in the search for Ashya King.
The information has taken the international hunt to the Costa del Sol city, where the family have 'strong links'.
The youngster was taken out of Southampton General Hospital by his parents on Thursday without doctors' consent.
The child is suffering from a brain tumour and is in need of 24-hour-a-day care. He is in a wheelchair and is fed through a tube, but it is thought the systrem's battery was due to run out last night.
He has undergone 'extensive surgery' for the aggressive tumour, with his last operation eight days ago, police have said.
But Brett and Naghmeh King have refused to accept their son's fate, with a family friend suggesting they 'ran away in desperation'.
Speaking outside Hampshire Constabulary's headquarters this afternoon, Assistant Chief Constable Chris Shead confirmed the force had obtained the warrant and were considering sending officers from Hampshire to assist Spanish police in Marbella.
He said: 'I can confirm we have obtained a European arrest warrant. What that will do is, when we find Ashya and his family, it will allow us to talk to his parents about what happened. Clearly we need to find out what their motive is in taking Ashya.'
'It purely gives us the power to arrest and then we'll be able to speak to them.
'Our message to Brett and Naghmeh is that this should not deter you from coming forward, please just come and speak to us.
'Once we know Ashya is safe, we will consider all other issues. Our first concern is to find him.'
He also called on British ex-pats in Marbella and people with business links in France and Spain to help spread the appeal to find Ashya.
Mr Shead added that health experts believe Ashya has a 'good chance of survival' but only if he is given professional medical care.
Officers now believe Ashya’s family has taken steps to be able to feed him, but said the feeding system was 'complex'.
He said: 'I would appeal to Ashya’s family not to think that they are able to administer this care themselves.
'The doctors assure me that proper medical training is required for the level of care that Ashya needs.
'I would also appeal to the medical profession, particularly in Spain, to contact the Spanish authorities if they feel that Ashya’s family have presented or made enquiries at medical facilities.
The couple and their seven children, aged from two to 23, boarded a cross-Channel ferry to Cherbourg, France, at 4pm on Thursday, triggering a police alert and a race against time to find them.
The family, from Southsea, are travelling in a grey Hyundai I800 Style CRDI, registration KP60 HWK.
Ashya is likely to be in a wheelchair or buggy, he cannot communicate verbally and is immobile, police have said.
The search widened considerably yesterday as Interpol sent out a missing persons alert to each of its 190 member countries.
Earlier today, officers from the UK are said to have spoken to a judge in Marbella to coordinate the search.
The complex on the outskirts of the city has 69 apartments, two swimming pools and views of Gibraltar.
A spokesman for Spain’s National Police, which manages Europol alerts, said: 'We have received an alert about the family and are actively trying to locate them.
'One of the areas we are focusing on is the Costa del Sol because we know they own property there and have friends in the area.'
They have also been contacting every single hospital in western Europe to see if a boy matching Ashya's description has been brought in.
A family friend said the couple had discussed taking their youngest son abroad in the hope of finding a cure, adding: ‘It seemed like desperate talk from a desperate family. Who wouldn’t want to try everything? But I never thought they’d go through with it.’
Assistant Chief Constable Chris Shead said: 'The need to find Ashya is now desperate. It is really important that we find him and ensure he receives medical attention at the earliest opportunity.
'We still don't know whether the King family have any spare batteries for the machine which administers food, the knowledge, or any way of recharging the battery.
'Without properly administered food Ashya's situation is very serious.We still urge everyone to please help us find him.'