There are some good books on this, but if you're new to Mormon history, I'd recommend starting with a biography of Smith, and if you're interested, you can keep going deeper. Any biography worth its salt will get into this.

First, the thing I remind everyone of when it comes to Mormon history is that almost every pre-1830 account is a reminiscence. We have only a tiny handful of contemporary records before the appearance of the Book of Mormon itself in 1830, and the founding of what became the LDS Church (and many splinter groups) in April 1830. Accounts of Joseph Smith as a money digger, a glass looker, and a treasure seeker came anywhere from a few years to decades later. The early years of Smith's life, from 1805–1830, contain almost no contemporary records. Even some of his earliest revelations, from 1828–1831, were lost and we have copies that were recorded into record books a few years later. However, there is enough correlation and enough information that we can assess these accounts of money digging with reasonable accuracy.

Smith was tried in 1826 of being a "disorderly person" and he was called a "glass looker" at the trial, and he was probably found guilty. There is a transcript of some of the trial records that were published in the 1870s—nearly 50 years after the trial itself—that were viewed with skepticism by the LDS Church. But original receipts from the trial were discovered from the judge and the constable (these receipts were requests for payment for overseeing the trial; judges were not full-time government employees at the time, but often traveling attorneys who would agree to trial work and then bill for it) at the trial. These receipts make it clear that Smith was charged with a crime, though there is some debate as to what the outcome of the trial was.

Other corresponding records come from affidavits collected by Eber D. Howe for his book Mormonism Unvailed [sic]. Howe's book, published in 1834, is important for historians of Mormonism because, while not exactly contemporary, it did collect statements from people who knew Joseph Smith directly within the past decade. These statements also establish that Smith was a treasure seeker. Taken with the trial records, these affidavits and other accounts paint a reasonably clear picture of Joseph Smith as someone who used seerstones to try and find buried treasure.

I'm going to digress for a moment and talk about the challenges of writing and discussing Mormon history, and touch on some historiography since a few questions have come up here due to the Last Podcast. First, even the word "Mormon" has become something of a stigma in recent years. Current LDS Church leaders have insisted that journalists and writers use the church's "proper" name, the Church of Jesus Christ of Latter-day Saints. But this is something of a solipsistic view: Joseph Smith's church led to the creation of dozens, hundreds perhaps, of splinter groups. The Utah-based LDS Church is the largest, but hardly the only one. The label "Mormon" is a common way to discuss the history of Joseph Smith's church and its splinter groups, and asking people not to do that erases those smaller groups. Second, the modern LDS Church, more than most religious institutions, gets its identity from its history. Believing Latter-day Saints are often very defensive of their faith's past; they tend to be far less invested in theology than they are history. Faithful Mormons who hear stories about Joseph Smith and polygamy, Brigham Young and racism, the Mountain Meadows Massacre, etc., can have a serious faith crisis that causes them to re-examine their most cherished beliefs. This is a major topic in the LDS Church today, and the church has responded by trying to be more open and honest about its history. But in the past, this has made it difficult, if not impossible, for historians to write about Mormon history without entangling themselves in apologetics and polemics.

What does all this have to do with Joseph Smith as a money digger and treasure seeker? At least a couple of things. 1) Mormons historically have labeled anything they deem unflattering about Smith or the LDS past as "anti-Mormon" or "persecution." The institutional church and its members have come a long way in the last twenty years, and this is less of an issue than it used to be, but it's still a major challenge. So those affidavits in Eber D. Howe's book that talk about Smith as a money digger? Persecution. Those later transcripts of the 1826 trial? Probably made up or forged. In other words, otherwise reasonable historical sources become contested. 2) Smith used a seerstone to treasure seek and try and find buried gold. He also used a seerstone to translate the Book of Mormon. The Gold Plates he said he obtained to translate the Book of Mormon were dug up from a hill near his home. So Latter-day Saint apologists have often tried to portray Smith's money digging as a youthful indiscretion that he left behind and then he separately went on to become a prophet. But for historians, it's much more difficult to separate Smith's money digging and treasure-seeking from the coming forth of his religion. Here is someone who, in 1826, was charged with fraud for telling people he could dig up gold with a seerstone. Then a year later he said he...dug up gold and then used a seerstone to translate the plates. The accounts in the LDS Church's scripture of the founding of the church collide with a messier historical reality. It can become very fraught.

Here's some additional reading:

Start with a biography or two on Smith. For a full biography, try Richard Lyman Bushman, Joseph Smith: Rough Stone Rolling (New York: Knopf, 2005). If you're more interested in Smith's early life and the church's founding, go with Richard S. Van Wagoner, Natural Born Seer: Joseph Smith, American Prophet, 1805–1830 (Salt Lake City: Signature Books, 2016). Now, if you really want to dive into the treasure-seeking, go with D. Michael Quinn, Early Mormonism and the Magic World View, 2nd ed. (Salt Lake City: Signature Books, 1998). Quinn provides a lot of context for magic in early American history, but it's a dense book and (IMO) he spends far too much time in the text and footnotes responding to polemicists critical of his previous work.