شكرا عالمساعدة.

Because in Levantine writing, this is often a shortened colloquial spelling of على المساعدة.

It breaks down like this:

• على = on / for
• المساعدة = the help

In everyday Levantine, على الـ often becomes عالـ in writing and speech, so:

• على المساعدة → عالمساعدة

This is very common in informal text messages and casual writing.

It is closer to colloquial Levantine because of عالـ.

Compare:

• شكرًا على المساعدة = more formal / MSA-style
• شكرا عالمساعدة = casual Levantine-style writing

So the sentence mixes a very common general Arabic word, شكرا, with a specifically colloquial Levantine contraction, عالـ.

A simple pronunciation guide is:

shukran ʿal-masāʿade

A few notes:

• شكرا = shukran
• عال = ʿal
• مساعدة = roughly masāʿade in a careful pronunciation

The letter ع is the hard part for English speakers. It is the consonant called ʿayn, a sound made deep in the throat. If you cannot produce it well yet, learners are often still understood if they say something close to al or aa, but it is good to keep practicing.

Both represent the same word, shukran.

• شكرًا includes the full formal spelling with the tanwīn marker
• شكرا is the very common everyday spelling without the diacritic

In normal informal Arabic writing, especially messages and chats, people usually omit diacritics, so شكرا is completely normal.

After شكرا, Arabic commonly uses على to mean for in expressions like thanks for ...

So:

• شكرا على المساعدة = Thanks for the help

Even though على often literally means on, in this kind of expression it is just the normal Arabic choice after thank you.

Yes, absolutely.

Both are understood, but they feel a little different:

• شكرا على المساعدة = more spelled out, more standard, a bit more formal
• شكرا عالمساعدة = more casual, more colloquial, very natural in Levantine

So if you want safer all-purpose Arabic, use شكرا على المساعدة.
If you want a more everyday Levantine feel, شكرا عالمساعدة is great.

It is not stated, because Arabic often leaves it out when it is understood from context.

English says:

• Thanks for the help

There is no you there either, unless you say:

• Thanks to you for the help
• Thanks for your help

Arabic works similarly. If you want to mention the person directly, you can add:

• شكرا إلك عالمساعدة = Thanks to you for the help / Thanks for your help
  in Levantine
• شكرًا لك على المساعدة = a more standard version

المساعدة means the help.

It comes from the noun مساعدة, meaning help or assistance.

The الـ at the beginning is the, so:

• مساعدة = help / assistance
• المساعدة = the help

In English we often just say Thanks for help sounds wrong, so we say Thanks for the help. Arabic here works similarly.

Because spoken Levantine often compresses small common words.

So:

• على الـ becomes عالـ

This kind of contraction is very normal in speech. It makes the phrase faster and smoother.

You may also see related casual spellings like:

• عالمساعدة
• ع المساعدة

Both are trying to represent the same colloquial pronunciation.

Here it is pronounced.

That is because م in مساعدة is a moon letter, not a sun letter. So the l sound of الـ stays:

• المساعدة = al-masāʿade

And with عالـ, you get:

• عالمساعدة = ʿal-masāʿade

If the next letter were a sun letter, the l sound would assimilate instead.

Yes. شكرا عالمساعدة works perfectly well by itself as a complete thank-you.

You can also make it warmer or stronger:

• شكرا كتير عالمساعدة = Thanks a lot for the help
• يسلمو عالمساعدة = a very common Levantine-style thank-you
• ميرسي عالمساعدة = also very common in Levantine speech

So the basic sentence is natural on its own, and you can expand it depending on how warm or casual you want to sound.