Text message regarding lost phone from ‘Apple security’

It is not Apple contacting you, that is 100% certain.

Most likely someone found(or stole your phone) and now they are trying to get your password so they can unlock it.

Take a look at these articles

Recognize and avoid phishing messages, phony support calls, and other scams - Apple Support

Identify legitimate emails from the App Store or iTunes Store - Apple Support

Hope this helps!

The texts look like scams to me. Ignore/delete them. Don't input any data. If you didn’t enter data, you don't have a problem.

If you entered password-related data, 

Change your Apple ID password https://support.apple.com/en-us/HT201355 

Here is What to do after you change your Apple ID or password https://support.apple.com/en-us/HT204071

If you did anything that might result in you being charged, the follow up with your credit card company, etc.

To be proactive, learn about phishing, scams, and Apple practices, etc., see:

If you see apple.com/bill, itunes.com/bill, or an unfamiliar charge on your statement https://support.apple.com/en-us/HT201382

Identify legitimate emails from the App Store or iTunes Store https://support.apple.com/en-us/HT201679

How to avoid scams when using Apple Pay to send and receive money https://support.apple.com/en-us/HT208226

This scam related information from Apple including reporting scams to Apple see Avoid phishing

emails, fake 'virus' alerts, phony support calls, and other scams https://support.apple.com/en-us/HT204759

How to identify scams related to purported apple notifications—per Eric Root.

“Apple will always address you by your name or the name they have on file for you, not Dear Customer, Dear Client or by using your e-mail address. The e-mail will be from @apple.com or @iTunes.com. E-mail addresses can be spoofed. You can go to Mail/View/Message/Show all Headers to see more. Apple emails won't have poor grammar/misspellings. Apple e-mails will never contain an attachment. Apple will never request personal information by email such as Social Security numbers, your Mother’s maiden name or full credit card numbers. …The only exception to the above I have noticed is if you order something from the Apple Store (apple.com), your receipt will be addressed to Dear Apple Customer. That is a receipt for a purchase you initiated.”

Stop “worrying” and start thinking like somebody that wants to unlock Activation Lock and greatly increase the value of an iPhone lost/stolen from somebody that might be unwary and unaware or scared, and that would like the lost/stolen iPhone back.

How would Evil YOU get YOU to give away your Apple ID password?

How would Evil YOU trick YOU into clicking on a link and signing into a fake Apple portal?

How would Evil YOU appeal to YOUR trust, and your openness?

Email source addresses can be easily faked. Calling telephone numbers can be faked, too. How would Evil YOU use a fake calling number to convince YOU to trust Evil You, ?

Scams are endemic. Folks think their iPhones and computers are prone to getting hacked, and while that’s within the realm of possibilities, it’s far easier and more effective to hack US than it is to to hack our devices.

Some related reading:

Recognize and avoid phishing messages, phony support calls, and other scams - Apple Support

They won't get any information from you replying other than what you replied.

Don't open any links they send.

They probably have your number from you entering in "contact me at XXXXXX if found" when you marked your iPhone as lost.

Just keep ignoring the messages.

You are being phished by a very active phishing community, probably acting at the behest of the person who actually found your phone. In all likelihood, someone found your phone and searched for a service that can "Unlock any iPhone for $100". These people then set to work to trick you into revealing your credentials.

Some quick research reveals that these same people are also actively phishing for PayPal credentials. They have many phony domain names with variations on apple-support and pavpal (Note the misspelling). It is good that you didn't give them any information.

You should probably change your Apple ID's password just to be on the safe side.

See all the posts above.