From ver1.5, google mymap+ supports the url-scheme. (ver1.5 will be released around 10 June 2012)
This section describes the format.

Case1: Add marker
mmplus://?cmd=addmarker&address=1418 Leonard St Manhattan, NY 10013 US&title=MarkerTitle&detail=MarkerDetails

Case2: Direction search
mmplus://?cmd=navi&address=1418 Leonard St Manhattan, NY 10013 US

Case3: Show the map
mmplus://?cmd=map&address=1418 Leonard St Manhattan, NY 10013 US

Parameters

mmplus://	scheme name
cmd *required	addmarker Add the marker to the specified address. navi Start navigation guide to the specified address. map Show the map of the address you specify.
address *required	Please be sure to Url Encode.
title	Title of the marker. Title is required only if the cmd is "addmarker". If not specified, it will be "NO-TITLE". Please be sure to Url Encode.
detail	Detail of the marker. Detail is required only if the cmd is "addmarker". If not specified, it will be empty. Please be sure to Url Encode.