Punctuations with relative pronouns

With and without the comma are both grammatical, but have different meanings.

Without the comma it is a defining (or restrictive) relative clause, which narrows the definition. The sentence means something like:

Sogou is a Chinese search engine, and is capable of searching text, images, and maps (as opposed to some other search engines).

With the comma it is a commenting (or non-restrictive), which does not affect the definition, but gives some additional information. The sentence with the comma means something like:

Sogou is a Chinese search engine. Incidentally, it can search text, images and maps (but I'm not saying anything about whether other search engines can do so: maybe they can, maybe they can't. I'm not distinguishing this one, just commenting that it can).

No, in this case "which" begins a defining relative clause (conveys important additional information about the search engine), that's why a comma is not needed here. You can substitute "which" with "that", which you can't do in non-defining relative clauses.

I disagree with the previous answers and would say that you have not provided enough information for us to answer the question definitively.

It is not clear whether you intend it as a defining clause or as a descriptive clause.

Defining clause

In this instance, you want to convey that the fact that it can "search text, images, music and maps" is an important distinction between this search engine and other search engines. That piece of information is critical to want you are saying. If that is your intent, then I largely agree with the answer from @Vilmar but would go further:

The comma is not merely "not needed", it should be omitted. Including the comma changes the meaning.
Yes, you can use "that" instead of "which", and that would make the intention clear.

So, if your intention is a defining clause, use:

Sogou is a Chinese search engine which can search text, images, music and maps.
Sogou is a Chinese search engine that can search text, images, music and maps.

Describing clause

On the other hand, if your main point is that "Sogou is a Chinese search engine" and the additional information that it can "search text, images, music and maps" is optional & incidental to mentioning the search engine's name, then you want a descriptive clause, and the comma is required: