As hard as I tried to catch up with him I just couldn't, so I called the police.
I ran after him as fast as I could but I still couldn't catch him, so I called the police.
1) As hard as I tried to catch up with him I just couldn't, so I called the police.
「追いかけても追いつかないから警察に通報した。」
一生懸命何かをしてもできない時は、As hard as A try to ~ A just couldn't. を使って言えると思います。
2) I ran after him as fast as I could but I still couldn't catch him, so I called the police.
「できるだけ早く走って彼を追いかけたが、捕まえられなかったので警察に通報した。」
run after 人 で「人の後を追う」
as fast as I can で「できるだけ早く」
catch 人 で「人を捕まえる」
ご参考になれば幸いです！
日本 
