I searched.....

They are both correct and share the same meaning.

In both sentences a pen is being searched for in an office.

They are both correct... but they have slightly different meanings.

The first sentence states that you searched the office for a magic pen (that may or not be there).

The second sentence states that there is a magic pen in the office... and that you searched for it.

Really? I read the second sentence as, there may be a magic pen in the office. There is no proof that it is there. It may be in the hallway or somewhere else. The person is checking the office for the pen, with hope that it is there. For all we know, they may have searched in another room before looking in the office.

I suppose it is ambiguous.

In Trader Joe's, they hide a little stuffed bee for kids to find to win a prize. I would say "We searched for the Bee in the Trader Joe's" to represent that there is guaranteed to be a bee somewhere in the store... and we were going to find it.

In the case where the magic pen may or may not be in the office... I would use the first sentence.

There is a difference in meaning to be sure when those two different meanings are being expressed.