I worked these chords out using the Guitar Pro tablature here: http://www.ultimate-
guitar.com/tabs/b/blink_182/im_lost_without_you_guitar_pro.htm
It's not exactly how the piano goes, but I used my ear to get the right chord from 
the root note. ANYWAY,
And this is how I play it.

It's capo on 2. If you don't own one, they're cheap and definetely worth it.
Chords used:

G
|-3-|
|-3-|
|-0-|
|-0-|
|-2-|
|-3-|

D/F#
|-3-|
|-3-|
|-2-|
|-0-|
|-0-|
|-2-|

Em7
|-3-|
|-3-|
|-0-|
|-2-|
|-2-|
|-0-|

D/A
|-3-|
|-3-|
|-2-|
|-2-|
|-0-|
|-x-|

Dsus4
|-3-|
|-3-|
|-2-|
|-0-|
|-x-|
|-x-|

Bm
|-2-|
|-3-|
|-4-|
|-4-|
|-2-|
|-x-|

Cadd9
|-3-|
|-3-|
|-0-|
|-2-|
|-3-|
|-x-|

Intro:
G-D/F#-Em7-D/F#

Verse 1:
G            D/F#         Em7       D/F#
I swear that I can go on forever again
G            D/F#              Em7          D/F#
Please let me know that my one bad day will end
Em7       D/F#         G            D/A
I will go down as your lover, your friend
Em7          D/F#          G              D/A
Give me your lips and with one kiss we begin

*awkward rest*

Chorus:
G                        D/F#
Are you afraid of being alone
        Em7     D/F#
Cause I am, I'm lost without you
G                            D/F#
Are you afraid of leaving tonight
        Em7     D/F#
Cause I am, I'm lost without you
*end chorus on G*

Verse 2:
Em7           D/F#           G         D/A
I'll leave my room open till sunrise for you
Em7          D/F#           G          D/A
I'll keep my eyes patiently focused on you
Em7           D/F#           G             D/A
Where are you now I can hear footsteps I'm dreaming
Em7        D/F#               G           D/A
And if you will, keep me from waking to believe this

*a little shorter awkward pause*

Chorus:
G                       D/F#
Are you afraid of being alone
        Em7     D/F#
Cause I am, I'm lost without you
G                           D/F#
Are you afraid of leaving tonight
        Em7     D/F#
Cause I am, I'm lost without you

*play chorus progression twice over (no vocals)*
 -end on G for one bar then play bridge

Bridge:
G-D/F#-Em7-Dsus4
G-D/A-Bm-Cadd9

Chorus [X2]:
G                       D/F#
Are you afraid of being alone
        Em7     D/F#
Cause I am, I'm lost without you
G                           D/F#
Are you afraid of leaving tonight
        Em7     D/F#
Cause I am, I'm lost without you

*repeat chords about 8 times only singing the last:
"I'm lost without you"
of the chorus until the drum solo comes in.

Hope I tabbed it okay. Hit me up for any questions or corrections or whatnot:
sbell@abcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijk.com
Not kidding, that's actually my e-mail address. Copy+paste anyone?
:)