Cmake linker error with shared libraries - cmake

Question

Im having an error on a chain linking, I've read lots of post but can't find a solution.
I build 3 libraries, in separated folders:
lib_1 as shared without dependencies
lib_2 as shared requiring lib_1 (build without problems)
lib_3 as shared that requires both lib_1 & lib_2
Here are the simplified CMakelists.txt (path have been simplified & triple-checked and mines are ok)
project (lib_1)
set (CMAKE_CXX_STANDARD 11)
set(CMAKE_BUILD_TYPE Release)
include_directories( lib_1/include/path/)
add_library(lib_1 SHARED lib_1/source/path)
====================================
cmake_minimum_required(VERSION 2.8)
project (lib_2)
set (CMAKE_CXX_STANDARD 11)
set(CMAKE_BUILD_TYPE Release)
include_directories( lib_2/include/path/)
add_library(lib_2 SHARED lib_2/source/path)
add_library(lib_1 SHARED IMPORTED)
set_property(TARGET lib_1 PROPERTY IMPORTED_LOCATION "lib_1/path/file.dylib")
=============
cmake_minimum_required(VERSION 2.8)
project (lib_3)
set(CMAKE_CXX_STANDARD 11)
set(CMAKE_BUILD_TYPE Release)
include_directories( lib_3/include/path/)
add_library(lib_3 SHARED lib_3/sources/path)
add_library(lib_1 SHARED IMPORTED)
set_property(TARGET lib_1 PROPERTY IMPORTED_LOCATION "/lib_1/path/file.dylib")
add_library(lib_2 SHARED IMPORTED)
set_property(TARGET lib_2 PROPERTY IMPORTED_LOCATION "/lib_2/path/file.dylib")
Funny thing is I think that add_library & set_property of lib_3 do nothing as removing the line doesn't change the error, i.e. I'm not doing what I should...but I've no idea anymore.
(Side note code runs smoothly if I build all files at once, but I'm trying my hands at shared libraries)
Error for reference:
[100%] Linking CXX shared library lib_3.dylib
Undefined symbols for architecture x86_64:
"LIB_1 function", referenced from:
in lib_3.cpp.o
[...]
Followed by all lib_1 & lib_2 functions marker as undefined