I've found on the AT&T homepage that they say
"Don't see what you're looking for?"
The omission of the subject is on purpose for friendliness, correct? I feel it's friendlier than "Don't you see ~?"
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The answer is covered in detail by this stackexchange article, referencing a PhD dissertation.1
This is due to a phenomenon that occurs in intimate conversational spoken English called "Conversational Deletion".
(1.19) No need to get upset about it.
(1.20) Been in Ann Arbor long?
(1.21) Ever get a chance to use your Dogrib?
(1.22) Ever get to Japan, look me up.
The phenomenon can be viewed as erosion of the beginning of sentences, deleting (some, but not all) articles, dummies, auxiliaries, possessives, conditional if, and [most relevantly for this discussion] subject pronouns. But it only erodes up to a point, and only in some cases. Whatever is exposed (in sentence initial position) can be swept away. If erosion of the first element exposes another vulnerable element, this too may be eroded. The process continues until a hard (non-vulnerable) element is encountered. In general, exposed first-person subjects are vulnerable in statements, and second-person in questions, and any exposed pronoun is vulnerable if it is recoverable from later in the sentence.
Next, is this usage "friendly"?
As noted in the comments:
The contraction is somewhat less formal, but no more friendly.
Well... one may consider that "informal" and "friendly" have some overlap in their meanings. They are not synonyms, but they are still similar, and so you are on the right track to view the text as "friendly".
They're using an informal shorthand. It's been popularized by emails, text messages, and instant messages to the point where it seems acceptable in a business context as well. All the same, the register that they're using is intentionally chatty and personal.
Like Sam said, StackExchange's main English site has an answer that talks about this at length from a (former?) professor discussing a paper one of his students published in 1974. They called this kind of speech conversational deletion, but it's more commonly known as ellipsis.
Incidentally, in this case,
Don't see what you're looking for?
. o O (No, I don't. Thanks for asking.)
is pretty much the only form of that question that works.
Don't you see what you're looking for?
. o O (No, I don't. What a badly designed site.)
is a form of the question that pretty much implies that you should be able to find it by yourself already. Anyone who would need to click that button would be peeved by the phrasing.
You don't see what you're looking for, do you?
. o O (WTF?!)
[changes their ISP & begins posting diatribes against AT&T on reddit]
is basically trolling the customer, implying that the page is monitoring their cursor and eye movement and has come to the conclusion that it's dealing with someone who is incapable of taking care of this themselves.
To find something formal and inoffensive, you'd have to remove the question entirely and replace it with something like 'Click here for other options'. That's far less personal and, yes, friendly.