my sister probably has bpd. sometimes she runs away and doesn't respond to calls etc and we don't know how to find her. now im alone at home because my parents are at the police station because we cant find her again

how do i prevent this? i dont know what to do, im barely 18 and shes 16, im alone here crying because i cant do anything when this happens, i send her messages, call her etc but she never responds, i know shes online because they get delivered... 

is this what mania is?? i know i shouldnt make this about me but i have problems too, part of our trauma is the same because we have both experienced certain things

everytime she does these things i always think the worst, that maybe she's going to kill herself, maybe someone will do something to her... i dont know