Okay, so me and my cousin are having this big "debate" about that happened in the movie. Long stoy short, she thinks the Decepticons followed Sam to Chicago and I think Sam followed the Decepticons to Chicago. I know I'm right but she just wants to be proven otherwise so who is right? Okay she decides that she needs to shove in some kind of comment so this is her: "I just watched the Transformers movie and I am rightttt. also, Bumblebee is the besttt! And if you guys are nice then be on my side .(;"
Well, techinically they didn't follow anyone, they simply triggered the Pillars in a convient place [i.e where Dylan's "HQ" was located], and used the Decepticon Forces to make a fortress of Chicago [thus no one would interrupt them or know what they're doing]. Sam followed them because he wanted to find Carly. Simple.
Well, the Decepticons were there first. After all, they all made a big deal about Sam going into the warzone.
decepticons picked chicago randomly. sam went there to save carly after tracing dylans call. nobody followed anybody. EDIT: well, in some sense sam followed dylan...
Sam followed them to Chicago. He even mentions in the movie how it's going to take 15 hours to get there. It wasn't random... Dylan had an apartment there.
Sam tracked Dylan to Chicago to find Carly, which is where the Decepticons also were. So technically, Sam did follow the Decepticons to Chicago. Your cousin is wrong. You win.