Who do Johnny and Ponyboy look for after they kill Bob?

After Johnny and Pony accidentally kill Bob Sheldon, they
are completely freaked out and they think they need to run away so they do not get
arrested.  What they do then is they go and look for Dally.  So the answer to your
question is Dallas Winston.

They figure that Dally is the
member of the gang who has been in the most trouble and he would be the one who is most
likely to be able to help them escape.  Johnny is the first to think of it -- he says
Dally can help them.  Pony agrees, thinking that Dally can do
anything.