Retrying Lost

我的钥匙丢失。我在看底下一个沙发。
I lost my keys. I will look under the sofa.

我的钥匙不见了, 我会看一下沙发底.

Retrying Lost

我的钥匙丢失了。，我在要看看底下一个沙发底下（有没有）。
I lost my keys. I will look under the sofa.

In Chinese, we put preposition after the noun that it relate with. So, "under the sofa" should be "沙发底下" :)

Retrying Lost

I lost my keys. I will look under the sofa.

标准译法：我把钥匙弄丢了，我要去沙发底下找找。

"弄"means you are initiative，钥匙是被你弄丢的。
“要去”means you will do something.
“在”means you are doing something.

Retrying Lost

I lost my keys. I will look under the sofa.
我的钥匙丢失了。我去在看底下一个沙发底下找找。
注解(Note)：丢失 is more fomal than 丢了，在 means  you are doing sth, 去 means you are going to do sth, slightly.  If we lost sth, we use 找(zhao)  to explain' look  for'.