"Už ho hledáme sedm dnů."

Translation: We have already been looking for him for seven days.

[DOette]

I think it may be less formal to place the adverb in the middle of the complete verb phrase.

[BoneheadBass]

I don't quite understand your comment, but there are nearly 300 acceptable translations for this sentence. What did you have in mind?

[Ajax737858]

'We have been looking for him already for seven days' is perfectly acceptable in British English but keeps being rejected...

[AgnusOinas]

I have added this word order now.