The headline is pretty bad and I think the parents are massively overstating it. On the other hand, if there is genuinely evidence (such as the girls' computers) that is not being checked instantly, as it should be, but only after severe pressure has been applied, then the police aren't really doing as much as they can and that's not at all what is needed. Perhaps many people no longer care too much about these girls ("they've made their choice", or words to that effect) -- but a full investigation of the case may help to provide better guidance as to what to look for in future.
As to going to Turkey -- if the girls are already in Syria, and I thought they were, it's not all that productive for the police to be in Turkey and as long as there is full and open communication with the Turkish authorities that is enough. I can understand the parents wanting to go to try and find their children, but I don't think it will achieve much more than just making them feel that they are doing something.