cannot find -lgtest when setting up Google Test

I'm using Google Test for C++ and trying to set it up on my linux machine. My make file has the following code:

CC=g++ 
CFLAGS=-I $(GOOGLETESTDIR)/include -L $(GOOGLETESTDIR)/lib -lgtest -lpthread -Wall
DEPS=fib.h
OBJS=fib.o main.o

all: | r6

clean:
    -rm -f r6 $(OBJS)

%.o: %.cpp $(DEPS)
    $(CC) -c -o $@ $< $(CFLAGS) 

r6: $(OBJS)
    $(CC) -o $@ $^ $(CFLAGS) 
.PHONY: all clean

I get the error when I run make:

/usr/bin/ld: cannot find -lgtest

How do I fix this? I'm new to this kind of testing and rather new to linux so I'm really lost.