How do I forward iMessages from my computer to my Android phone?
There are a number of third party solutions to this problem which the first party (Apple) has never resolved. Most of them involve forwarding your messages to a server somewhere, where they'll use a cell phone gateway to forward them as SMS to a phone you choose. Obviously, this represents a significant security vulnerability, as whoever owns the server has full access to your messages which could contain sensitive information. 

The only way around this vulnerability is to own the server yourself, which is basically what PieMessage does. It's an open source project hosted on Github, also available on the App Store somewhere. I haven't actually tried it out yet -- I don't have an iMac that stays at home all day to use as the server -- but it seems to have trusted reviews.