Some neck pain can come from muscles further down the back, particularly ones that run down near the inner edge of your shoulder blades.
A good way to self massage these is to use a tennis ball against a wall. You can roll the tennis ball between the wall and your back and get quite good relief.
Try to identify trigger points. These are small points that are extra tender and are the key to getting your muscles to let go. If you can identify these and roll the tennis ball around on them it is great. It also works with these trigger points to just press against them if they are too tender to massage.
The tennis ball also massages general muscles well too.
It is also possible to massage the muscles along the top of your shoulders with a tennis ball by rolling it between a door jam and your shoulder muscle.
It's just another silly looking thing to do but hey all those people doing exercises in gyms or doing other activities like tai chi look strange too if you really think about it

P.S. A lot of tension headaches can also be relived by massaging these trigger points. It is amazing to feel a loosening above your eye or in your eye socket or on your skull by massaging trigger points in your back.