try to think where she goes when she wants to be alone
Call the police, meanwhile gather some people to go find her -- first search some places she tends to go, then look deeper.
If that makes sense.....
I assume you guys called the police already? I would drive to spots she likes to go and look for her. I think they have that 24 hour missing thing. But, hell if it would stop me from looking before that.
report that fact and issue a search around the waters of high bridges, the bottom of cliffs, and check her purchase records to see if sh has purchased any rope, a chair, or a gun or poison
Call her parents or the Police