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.
who johnny and ponyboy look for after they kill bob, is dally because they know that he knew a way to a "safe home" to hide out.
After Johnny and Ponyboy kill Bob by the fountain, they go looking for Dallas Winston. Johnny comes up with the idea, and Ponyboy agrees because Dallas has talked of such things when he in New York.