My main instrument is guitar. I have found that many popular songs that were written on piano (or keyboard) where the keyboard arrangement is the backbone of the recording - the guitar charts (guitar chords or tab) available online - often do not sound correct at all.
As a composer and songwriter myself (who can't sight read standard music notation) I create almost all of my music using a guitar. I can play enough keyboard to understand that the instrument lends itself to creating arrangements that sound very different than what the guitar leads a composer to produce. For more detail on why this is true check out the answers to This Question on Stake Exchange Music.
When I want to learn to play a piano based song on guitar and there are no decent guitar tabs or guitar chord charts available online, I create my own arrangement. Below I will describe the process I use.
If piano sheet music or standard notation music is available for the song, I start with the key signature. Many piano based songs are written in keys that are not commonly used in guitar playing (because they contain few open chords or chords that are more difficult to play) so I might have to transpose everything to a guitar friendly key for the chord set and then use a capo if I want to play in the same key the piano music is written in. The key signature will narrow things down to one minor and one major key. Other clues will allow me to determine if it's major or minor. This Link will describe how to use the Key Signature together with other elements in the sheet music to determine if the key is major or minor. Once I know the key the sheet music was written in - I can transpose all the notes into my guitar friendly key so I can have a set of notes to work from. Most of the time, any chords used in a song will be comprised of the notes used in the song.
Once I have a key, I know what chords I have to work with that are common to that key. A good guess for the first chord would be the I chord (one chord) which is the chord that corresponds to the key. If that chord does not sound correct, I will try others. The notes in the melody or in the bass line, are usually good clues as to which chord is played over that section of the song. Even if you can't immediately identify what chords are being played in the recording, you can tell when the chord changes occur and make a note of it. It's mostly a trial and error process for me, trying different chords to see what sounds correct.
If I have transposed to a guitar friendly key, and I am listening to the original recording as a guide, I will use a capo to put my guitar friendly chord set in the key I am listening to so I can play along with the recording. I have found that it's often more obscure less common (diminished, suspended, augmented, etc) chords that best replicate what I am hearing the keyboard play on the recording.
If the song has lyrics, I will print (or create a word document on my computer) the lyrics in a format that matches the various measures found in the sheet music or recording. Then I can make a mark wherever a chord change occurs and as I discover the correct chord, write it above the corresponding words in the lyric sheet.
It's a process, there is no shortcut - but one does not have to be able to become proficient with standard music notation or develop the ability to sight read and play from sheet music to do it. Below I have pasted examples of some tools I use as a "cheat sheet" while working it out.
Below is a Key Chord Chart for major keys. You can find similar charts online for minor and other keys as well. This chart shows the most common chords used in an arrangement written in a major key and will help identify which chords are used in the piano based arrangement. It will also help when you transpose those chords to a guitar friendly key when needed and makes it clear which keys are not guitar friendly.
This next chart will make it easier to find a capo/guitar friendly chord set combination that will match the key the piano based sheet music is in if not in a guitar friendly key.
This chart (below) is an example of a transposition chart that can be used to quickly transpose notes (and chords) from the original to a guitar friendly key.
Finally, this Chart from TrueFire.com is an example of a chord chart that (in addition to the common chords) shows how to play some of the less common chord types (suspended, augmented, diminished) that you may need in order to match a guitar chord to one used in a piano based arrangement.