If you have the IP what about doing a tracert to see where exactly it comes from? Though I'm guessing that may also give you roughly the same information as doing the whois and reverse lookups.
Not really it will give you the path and some hints on who owns it, whois will tell you who the space was assigned to by the registrar, so that's who is ultimately responsible for the ip in question. Whois also lists contact information to get in touch with someone (hopefully).
So for instance, lets talk bitcointalk.org.. -- 109.201.133.65
traceroute tells us thus:
18 30-239-159-85.rtr1.b06-s02-az16.gsa.nl.nforce.com (85.159.239.30) 106.420 ms 109.760 ms 109.593 ms
19 5-239-159-85.rtr1.dbn.nl.nforce.com (85.159.239.5) 120.049 ms 118.963 ms 119.622 ms
20 * * *
(probably filtered at this point)
whois however tells us this:
netname: NFORCE_ENTERTAINMENT
descr: Serverhosting
admin-c: NFAR
(...)
person: NFOrce Entertainment BV - Administrative role account
address: Gewenten 8
address: 4704RD
address: Roosendaal
address: The Netherlands
phone: +31 (0)206919299
fax-no: +31 (0)206919409
abuse-mailbox:
abuse@nforce.comnic-hdl: NFAR
mnt-by: MNT-NFORCE
source: RIPE # Filtered
(...)