1. look 用作系动词表示谈论暂时的外观时，可以用一般式或进行式，两者在意义上没有太大区别。如：

You look [are looking] tired this evening. 今晚你好像很累。

You look [are looking] a bit tired. 你看起来有点累。

My boy is not looking [doesn’t look] very well. 我的孩子气色不太好。

注意：look 后跟 like 或 as if 时习惯上不能用进行式。如：

她像她母亲。

误：She is looking like her mother.

正：She looks like her mother.

她好像在做梦。

误：She is looking as if she’s dreaming.

正：She looks as if she’s dreaming.

2. appear 和 seem 用作系动词时习惯上不用于进行时态。如：

他似乎相当富有。

误：He is appearing to be quite rich.

正：He appears to be quite rich.

在我看起来他好像很正常。

误：He is seeming to me quite normal.

正：He seems to me quite normal.

以上内容摘自英语语法网的以下文章：

http://www.yygrammar.com/Article/201203/2802.html 

另外英语语法网的以下文章也可以参考：

http://www.yygrammar.com/Article/201411/3742.html 

http://www.yygrammar.com/Article/200802/160.html 

http://www.yygrammar.com/Article/201212/3123.html