You must first find out wad's the person's IP address, after which, you can check up the person's IP address at this website:
http://www.completewhois.com/.
After the list of result had appeared, if the person's from singapore and you know which ISP he is subscribed to, you can send a report of abuse at the following website or email stated below:
Starhub -
[email protected] ( email add )
Singnet -
http://www.singnet.com.sg/tou/misc/ia_incidentreport.aspPacific Internet -
[email protected] ( email add )