Please help me locate a non paying ex for maintanence

Hi and thank you for reading my post. Hopefully somebody can help me? I am a single mother who is trying to find my ex for maintanence not that I got much I only ever recieved £5 a week yes a fiver which is ludicrous and now my ex has gone AWOL and even that has stopped! I've been in touch with CSA and they said they can't donothing as they are NOT an investigation authority and don't know the mans whereabouts.. Please help me as I know he is working 24/7 but cash in hand. I've notified inland revenue but as I amnot related to my ex I don't get told nothing!! Please point me to someone who can get results. Thank you

Please help me locate a non paying ex for maintanence