Je ne trouve plus mon identifiant pour me connecter au site.

Because ne ... plus means no longer / not anymore, while ne ... pas is the basic way to say not.

So:

• Je ne trouve pas mon identifiant = I can't find my username / ID
• Je ne trouve plus mon identifiant = I can't find my username / ID anymore or I no longer can find it

In this sentence, plus suggests that the speaker used to have it or be able to find it, but now cannot.

Also, in standard written French, plus replaces pas here. You do not say Je ne trouve pas plus in this meaning.

Yes. Literally, Je ne trouve plus means I no longer find.

That sounds a bit unusual in English, but it is completely natural in French. In real English, you would usually translate it more naturally as:

• I can’t find ... anymore
• I no longer can find ...
• I’m not able to find ... anymore

French often uses the present tense this way where English prefers can’t find.

Identifiant usually means a login ID, username, or some other identifying login information.

It is not the password. The password would be:

• mot de passe

So:

• identifiant = username / user ID / login
• mot de passe = password

Depending on the website or context, identifiant could refer to:

• a username
• an email address used to log in
• a customer/account number

Because identifiant is a masculine noun.

So the possessive adjective must also be masculine singular:

• mon identifiant = my username / my ID

Compare:

• mon mot de passe = my password
• ma connexion = my connection / login process

A useful reminder: the ending -ant in identifiant does not make it feminine. It is still masculine.

Se connecter is a pronominal (reflexive) verb, meaning to log in or to connect.

Its basic form is:

• se connecter

When the subject is je, it becomes:

• je me connecte = I log in

After pour, French uses the infinitive, so the reflexive pronoun stays with the infinitive:

• pour me connecter = to log in / in order to log in

So the structure is:

• pour
  • reflexive pronoun
    • infinitive

Examples:

• Je viens pour me renseigner. = I’ve come to get information.
• J’essaie de me souvenir. = I’m trying to remember.

Because in French, object pronouns and reflexive pronouns usually come before the verb.

So:

• se connecter = to log in
• me connecter = to log in myself / to log in

Even in the infinitive, the pronoun stays before the verb:

• pour me connecter
• sans me connecter
• avant de me connecter

This is normal French word order.

Because à + le contracts to au in French.

So:

• à + le = au
• à + les = aux

That gives:

• se connecter au site = to log in to the site

Other examples:

• au bureau = to the office
• au cinéma = to the cinema
• aux enfants = to the children

So à le site is grammatically incorrect; it must be au site.

Sometimes, but the meaning and usage are a little different.

With se connecter, French commonly says:

• se connecter à un site
• se connecter au site

That is the standard way to say to log in to a site or connect to a site.

Sur le site means on the site, and it is more about location or activity on the website:

• Je suis sur le site. = I’m on the site.
• J’ai vu ça sur le site. = I saw that on the site.

So in this sentence, au site is the better choice because the idea is logging in.

Both are possible, but they are slightly different.

• trouver = to find
• retrouver = to find again / recover / get back

So:

• Je ne trouve plus mon identifiant = I can’t find my login anymore
• Je ne retrouve plus mon identifiant = I can’t find my login again / I can’t recover it / I can’t locate it anymore

Retrouver can sound a bit more like you had it before and are trying to recover it.
Trouver is simpler and very natural here.

In careful speech, yes, usually.

With ne ... plus meaning no longer / not anymore, plus is often pronounced roughly like plu (without the final s sound).

So you often hear:

• Je ne trouve plus → plu

But pronunciation can vary depending on speaker, speed, and register.

A useful learner point is this:

• In negative expressions like ne ... plus, the final s is often not pronounced.
• But in other uses where plus means more, pronunciation may differ.

For a beginner, the most important thing is to recognize ne ... plus as one unit meaning not anymore.

In casual spoken French, many speakers drop ne and say:

• Je trouve plus mon identifiant...

Even though that literally looks like I find my ID more, in spoken French it is understood as:

• I can’t find my ID anymore

However, in standard written French and careful speech, you should keep ne:

• Je ne trouve plus mon identifiant...

So for learning and writing, the full version in your sentence is the correct model.

Here pour means to / in order to.

The phrase:

• pour me connecter au site

explains the purpose of needing the identifiant:

• my login ID to log in to the site
• my username for logging in to the site

So the whole sentence means that the speaker cannot find the ID that is needed in order to log in.

Yes. You could say:

• Je ne trouve plus mon identifiant afin de me connecter au site.

But that sounds more formal and less natural in everyday speech.

In ordinary French, pour is much more common and more natural here:

• Je ne trouve plus mon identifiant pour me connecter au site.

So learners should usually prefer pour unless they specifically want a more formal style.