I was looking for him all this time! / I was looking for him everywhere!
That's where he was! / I had no idea he was in that (kind of) place! / He was there the whole time / He was in(at)場所 the whole time!
「彼をずっと探していたの」＝ I was looking for him all this time! / I was looking for him everywhere!
「あんなところにいたのね！」＝ That's where he was! / I had no idea he was in that (kind of) place! / He was there the whole time / He was in(at)場所 the whole time!
※上記の「there/that's where」は文脈によって違う場所を表す。
「あんなところ」にあたるのが there / such a place です。
質問者様の文章になりますと
I was looking for you. You were there.
ずっと探していただから(have been )を使いそうですが、これはまだ見つかっていないの意味になってしまいますので、この場合は(am looking for)の過去形で。
イギリス 
日本 
