Q. Is there a scriptural commandment to look for the new moon? If so, where is it found? Thank you.
A. Yes. The word “observe” (shamar #8104) can have the meaning of "watch," “to look” and/or “take note of and keep.” The word "shamar" appears some 468 times in the OT (5 times as "watch") and has numerous translations to the English words: keep, watch (Vine's Expository Dictionary); keep, watch, observe, watch for, wait for & others (BDB Hebrew Lexicon). In Deut 16:1 - "Observe the month of Abib..." could easily read "Watch for the new moon of Abib..." To watch for means one must make a visual sighting.
When Yahweh took the people out of Egypt, He pointed out the new moon, after the new growth from the springtime, saying, “This month (new moon) shall be for you the beginning of months. It shall be the first month (new moon) of the year for you,” Exodus 12:2 ESV. It’s the only way to determine the new year and the appointed times of Yahweh (Lev. 23). Historical information by Jewish scholars (Edersheim, Spier, etc.) also show the practice of observing the new moons for each new month was done.
The link below has some additional information on new moons, but it appears that since Egypt had up to three different calendars (historical records confirm this), Yahweh wanted no mistake about when His biblical New Year started. The moon has the root meaning of "light" brought out, one must then watch/look/note/observe the first visible crescent light presented to be able to confirm a new moon. It would then be kept and noted as a new moon (new month).