A friend

So a friend of mine I’m a almost 100% sure is self harming and I’m not sure how to approach them about it in the past people normal came to me about it but I know this one won’t. After I moved school I haven’t felt really close with anyone even the people I hang out daily so it means this a little harder. I feel like my friend is really guarded and won’t say anything and I don’t want to make them overly anxious trying to talk to them along with their other stressors. 

Does anyone know how to like start a convo off or what I should say to them