Thanks sjm & everyone for sorting this out to get me in!
I don't know about being an 'official' rep, but I do have permission to spread the word as much as possible - the family members don't speak English
the links which have been posted already give pretty much all the information any of us have about this
She left home at 7:30am on 20th May to go to school. When she didn't return home it was discovered that she hadn't taken her schoolbag, & wasn't wearing a necklace & earrings which she habitually wore. Her father searched for her but when he couldn't find her he went to the police.
It was thought that she was more than likely in Koblenz, because the lad she had been spending so much online time with lives there, & he had apparently been planning a trip`to Spain. The assumption everyone seems to have made is that she ran away with him.
The latest info is that her father found a 'farewell letter' hidden in her bedroom a couple of days ago, over 2 weeks after she went missing. In it, she says that she was no longer in a relationship with the Russian lad who lives in Germany, & that she can't see the point of living any more. The police yesterday were searching a countryside area of the town - they had searched it before, but more seriously yesterday & more searches of other areas are planned.
The lad in Germany says that he hasn't seen her or had contact with her since before she went missing.
The phone signal in Sagunt after she went missing adds confusion, or suggests that she was headed out of Spain - Sagunt is between Jávea / Xàbia & the border of Spain & France
& yes, as someone else has said, it's easy to travel overland in Europe with no passport, nor in fact any other ID
Her parents have lived in Spain for 10 years, Khrystyna only joined them 3 years ago & her elder brother still lives in the Ukraine. This is actually a fairly common situation; the parents will come & get settled, leaving the children with family & sending for them when they can. The parents have said that Khrystyna has never really settled in Spain & this is borne out by classmates who say that she doesn't interact with anyone at all.