iMessage on Mac doesn't see Android phones

Because it's not a phone. In order to get SMS MMS messages on a Mac or iPad, you need an iPhone and you have to enabled Text Message Forwarding in Settings>Messages on the phone and linked it to your Mac and iPad.

OK, the answer is that you must use your iPhone as an intermediary to send/receive SMS text messages, and you can then use the iPhone's Handoff (Continuity) capability to connect those SMS messages to/from your Mac.

See the "SMS" section here:

Use Continuity to connect your iPhone, iPad, iPod touch, and Mac - Apple Support

when i had a 5s i could send and receive imessages on my imac. also from android.

Hi, actually the Android Phones runs on the "Google's Android" Operating System and on the other hand, the Apple runs on the IOS and the Apple's Macbooks runs on the Mac Operating System. So, there's a huge difference between these two operating system and both of them doesn't support each other's functionality.

You can check difference between them in this article.

http://itsdiscovery.com/android-vs-ios-which-one-is-better-and-why/

Is your iPhone receiving those texts?

no ipads or imacs have never been able to send sms's only iPhone can do that

and sms is the means of communication used when sending to non ios devices