I will tell you what I know, and I got this information from someone else and so far has seem to hold true.  Lil Timmy is a super rare spawn.  When he spawns, he walks in the canal district around the cathedral district starting from the south, through the cathedral area, and around to the north entrance.  Then he despawns.  He only sells one white kitten each spawn.  It is best to look for him after a server reset.

i stood on the bridge from the dwarven dist to the cathedral .. took about 2 mins and sure enough i was lucky to see him ... 12:50 pm EST..

My suggestions to anyone who wants a kitten or wants to sell it is to get fishing get a pole sit on that bridge start fishing and be willing to wait...

At around 12 midnight EST I saw him on the east side of the trade district, heading across the bridge, I snatched up a kitten and then fallowed, he looped up around the rest of the bridges and then took the route the others explain.

Just by luck I was browsing this very page, and when I alt tabbed back into WoW Lil'Timmy walked right infront of me... I bought the kitten from him...<Hugs the kitten> cute...IT was right at the southern bridge betwen the trade and Cathedral areas

The image size is too big no wonder it takes forever to load.

myself, i have once seen timmy on the old/ trade bridge as i was swimming in the canal... dont ask why i was there. anyways, i went up the very next set of steps and i lost him because i went INTO old, and he presumably went around it, dunno if that helps. probably doesnt tho sry if im not helping btw

hello again, This is Lil' Timmy's Route, i am not quite sure where he spawns but this is the best i can do. anyway, the red dot is where i saw him, and the red line is the route he took when i followed him.  i waited on that first bridge i saw him cross and i bought a cat.
Click for this small child's Route
-Ronar <Static Alliance> (server: Blackhand)

hello again,

I think the route linked to above might be one of two routes as looking at my map I found Timmy on Earthen Ring server on the canals just near the south exit of the cathedral area, which according to the route he doesn't go

Double post ~_~

I started to sit on the bridge by the cath at 11:08 PCT.  Moved to the one by the old town and dwarven.  Then moved to the one by trade dist.  I was 1 min from my time frame I was going to let my self sit here and readying the comments here when I looked down at my char and he was walking by..  Got the kitten and very happy camper here. It was 11:44 PST

Some newbie night elf gal said aloud on general chat "I'm new, does anyone have 60s for me to get a kitten?" So I asked "Yea, where are ya?" She said she was in the cathedral district, so I went there and bought the kitten and was about to run with it (knowing well how much it was worth)... Then I felt rly bad and gave it to her for free. Curse my generosity. Oh well, It gave me a fuzzy feeling inside. *sigh* I love helping out the nieve and innocent.

i found him heading towards the bridge between dwarven district and cathedral, i camped out on the bridge for no more than 5 minutes, i was looking at this site, maximized WoW and saw him 2 seconds later heading my way!Thank you guys so much, you helped me a bunch.

i just got a cat i found little timmy when he spawned at around 3:45 he followed the route xwhitemousex showed in the edited map the journey took aproxamately 5 mins and he despawned at 3:50 good luck to thouse wanting a white kitten

Today, wich is Sunday EST I saw Lil Timmy on the server Lightbringer. I found him in Cathedral Square at 12:53 pm server time. And the server was Lightbringer. I've seen Lil Timmy 3 times already. And I got the kitten! ^_^ I hope this helps!

I found him right were he spawns, he spawns by the bridge between the trade and old districts, then gos around old town, across the bridge between old town and the dwarven district, around dwarven district, acroos the bridge between dwarven and cathedral, across the cathedral quare, out of the western side, and despawns at the dead end to the right, against the wall.

It is a v cute cat, HAPPY HUNTING!

http://www.g4tv.com/cheat/features/51801/World_of_Warcraft_Secrets.html
this website gives you some info about lil timmy and also other easter eggs in WoW

He never seems to come when you want him to but when your not looking for him you always see him..ive bought 4 cats and kept one. then sold the rest at AH for 10g each!

I got the White Kitten after following kinirosenshi's map (shown above) backwards on only the second try, with about 15 minutes between attempts.

I didn't see where Lil Timmy spawned, but I ran into him as I was rounding the west corner of Old Town on the canal. It was at 7:01am PST on Blackhand (9:01am server time, CST). He must have just crossed the bridge between the Trade District and Old Town. Luckily he still had the kitten.

From reading all the posts so far, it looks like he spawns in at least two places, the end of the canal between Old Town and the Trade District (or on the bridge itself), and at the end of the canal on the west side of Cathedral Square. He definitely despawns at that spot on the canal at Cathedral Square as I followed him there, and everyone else seems to confirm that.

Have fun hunting!

Here are the things Lil Timmy said while walking along:

"Don't worry, I'll find a good home for ya."

"I can't believe dad won't let me keep your sister."

"Will someone please give my little kitten a good home?"

"Can anyone give my adorable, extra little kitty a home?"

"Kitten for sale, looking for a good home."

I followed the map direction and got Timmy my first time out.  Thanks to everyone who has posted their experiences.

Rionach, Devotion, Alleria Server

I had to borrow 48 bronze from a guy and then i fonud timmy 15-20 min later. I was wondering how much i could sell it for. I thought i cold sell it for 5 gold because that's what it say's on cheat!

Is there a specific spawn rate?

Still Waiting............Been 2 Hours :X

Are those times GMT or different?

I suggest you get a book, head over to cathedral square, at the exit that goes to the park around the time stated in other comments, and wait for timmy to spawn.  If your a hunter put on track beasts and look for a slow moving white kitten on the mini map.

He spawns were he despawns, against a wall to the west of the Cathedral on the canals. I waited 3 hrs and then when i logged Tada, someone sent me a mail in the mornin with one and said "heh i felt sorry because he spawned at 3 AM after you logged"

I finally was able to get a kitten from timmy.  Went straigt to the AH and put it up.  A minute or so later I was looking at my auctions to see if there were any bids.  Well, I made a big oops, bid starting 3 silver, buyout 5 silver.  Before i could cancel and correct it, my comp shut down and restarted.  Luckily no one had caught it before I got back in and canceled the potential super sale of timmy's kitten!

Look twice before posting you auctions.  I sure will!

I know you can buy the kitten from Timmy for 60s or so, but how much can you sell it for? How much would you get from a vendor and how much from an auction? Thanks in advance

Little timmy sells his cat for around 40-60s and you can sell it to any vendor for 5g!!!

Found him! and look at the time! (15:13) ^^
(the white kitten is standing behind him)
he's at cathedral square
a few minutes after he's been through cathedral  square he will despawn

I was waiting on bridge where everyone said: between old town and trade district. I was reading the comments on this page and decided to give up when he spawned right in front of me. Cheers for the tips guys! Bought it for 54 silver.