Sam really didn't want to surprise Fred by being the one to knock on her door. Then again, he thought that her apartment should be the first stop. They needed to know that she was okay and they would probably get the most information from checking out the scene of the... well, he wasn't sure if crime was the right word. The scene of the weirdness.
He also didn't like the idea of separating from Dean all that much either. If something was going on, then he wanted to be there to watch his brother's back.
Besides, for the same reasons that he didn't want to alarm Fred by knocking on her door alone, he also didn't want to be found skulking around her building.
"I think we should check out Fred's place together. Then if she isn't there, we start asking questions."
There was a silent plea in his eyes that Dean not just go his separate way here. That whatever they did with this case, they did it together.