Time to get some things clear. Slenderman has two kinds of powers: Phisical (Which can hurt us of afect us) and dimentional (which cannot hurt us nor afect us but we need to know in order to understand this.... Thing/creature. Over my last few entries i've been focusing on the dimentional aspect of him, this has lead to diferent conclusions, we already have quite a bit of information about him (Our information has not been tested but it's the safest assumption right now) which can put us in danger. Why? Slenderman is known to chase kids that are unlucky enough to find him (even after they grow up) AND those who actively search for him or about him. We know that he is somewhat able to locate anyone anywhere at any time, How? Does he feel summoned? Is knowing him enough summon for him? If so, how can this summon him? The truth is: We have no idea. Ivan said that it is possible that he inhabits a spaceless dimention, one in which everything ocurs at the same place. It is hard to imagine, but it is an explanation. Using the spaceless realm he is able to "Teleport". This one investigation is the first we have to give up. We don't find anything related and our assumptions are not enough since most of them are not possible.
Conclussion: Our guess is as good as any, we can't pinpoint the reason or method Slenderman uses to detect those who search for him.
As always, I beg for corrections (If needed) suggestions and observations. Sorry for the waste of time :(
Personal note: I also beg for any ideas on a topic. If I don't find anything new to investigate I'm going back to look into my oldest entries and try to correct/Remake them.