The Los Angeles-based 26-year-old currently has about 867,000 followers on Instagram. To reach the coveted 1 million mark, he is posting snapshots of famous faces bearing his makeup look, which he calls a “lit-from-within glow.” In return, some stars tag him in their own red-carpet looks, leading their followers back to his account.

One million followers on Instagram used to be a level only celebrities could aspire to. Now, entrepreneurs, musicians, budding artists and regular people are aiming to win a capital M next to their follower count. While Instagram, owned by Facebook Inc., declined to say how many accounts have 1 million or more followers, the number is a benchmark that can change a new band’s trajectory, encourage household-name status and provide an entree into the world of branded partnerships, fashion and product marketing and more.

At that number, “you’re at celebrity level when it comes to brand partnerships,” said Mae Karwowski, founder and chief executive of Obvious.ly, which connects popular social-media users, sometimes called “influencers,” with marketers. “You could have your own line with a beauty company. You can have your own line in a fashion store. You can be the celebrity face for campaigns.”

While influencers with as few as 10,000 followers can score marketing partnerships, the compensation is typically free products or up to $150. Once they reach 1 million followers, Ms. Karwowski said, the payments rise considerably, up to $15,000 per post and sometimes equity in the company.

Mr. Ta was motivated to build up his social-media following after seeing the success of other makeup artists on YouTube. He recognized the importance of Instagram in the image-obsessed beauty world early on, tagging makeup brands he used on clients in hopes of getting reposted. He got a taste of social-media fame in 2014 when he received an Instagram direct message from “Pretty Little Liars” actress Shay Mitchell. After he posted the photo of Ms. Mitchell to his account, he quickly gained 15,000 followers.

Now Mr. Ta posts one to three photos a day of his celebrity clients and interacts with followers through direct messages and comments—something he said is critical to boosting follower counts. He frequently answers questions about the products he uses and keeps active in the comments of his posts.

Ms. Karwowski pointed to fashion blogger Arielle Charnas, whose Instagram account is @somethingnavy, as an example of someone who has used the platform to maximum effect.

Ms. Charnas, 30, who has 1.1 million followers, in September began a campaign withNordstrom Inc.’s private label Treasure & Bond in which she helped design shearling coats, mules and off-the-shoulder sweaters for the brand.

A Nordstrom spokeswoman declined to say how many items sold as a result of the campaign but said “we are very pleased with our partnership with Arielle Charnas. Our customers love her and the product we produced together.”

Ms. Charnas began blogging in 2009, posting photos of her outfits and New York City life, but she quickly developed a following when she joined Instagram by using popular hashtags like #ootd and #fashionblogger and engaging with her followers in the comments.

“Every time I got to another 100,000 I would do a dance video to celebrate it,” said Ms. Charnas.

Other fashion accounts took notice and began reposting her images, further boosting her following and attracting attention from deodorant brand Secret, hair-care line Nexxus and activewear label Bandier. When she reached 1 million followers last March, she celebrated with family and friends with dinner and drinks.

“It was so cool to get that “1M” showing up on there,” said Ms. Charnas.

For musicians, Instagram provides another way to develop a following. The boy band Why Don’t We attributes its latest spot on iHeartRadio’s Jingle Ball tour to its 2.3 million Instagram followers.

The group, whose members include Jonah Marais, Corbyn Besson, Daniel Seavey, Jack Avery and Zach Herron, hit one million followers in July 2017 before releasing a complete album. Mr. Besson said the number encourages potential fans to hop on the bandwagon when they see how many other people already have.

“It’s a new age, and it’s not about record sales anymore or how many albums you can sell. It’s a lot about digital and online,” he said.

Mr. Seavey said the most popular photos are what he calls “personality posts” where the band is goofing off, including a Halloween one showing Mr. Besson dressed as a corncob. The caption: “they call me cornbyn.” It has been “liked” more than 250,000 times.

The Knot, a wedding website and magazine, said it became the first wedding brand to gain 1 million Instagram followers in July 2016. Kristen Maxwell Cooper, its editor in chief, said that having that many followers led to other opportunities, such as working with the bride-to-be behind @girlwithnojob, a popular Instagram meme account, on her wedding.

“We can help them get their name out to a different audience,” said Mrs. Maxwell Cooper.

Obvious.ly’s Ms. Karwowski said that being noticed and reposted by big Instagram accounts is crucial to gaining thousands of followers. Instagram users can tag clothing brands they are wearing or accounts they admire as well.

She warned against services that promise, for a fee, to add followers. Brands are checking for an “authentic” following, she said, and notice when the number of followers appears out of sync with the actual engagement and comments an account is receiving.

Buying or selling followers is against Instagram’s policies. The Federal Trade Commission is also scrutinizing how influencers use social media, sending warning letters to 21 of them last year regarding the brands they mentioned and what their financial ties were.

Some social-media users find follower success by dating the right influencer.

Fashion and travel blogger Lauren Bullen (@gypsea_lust) met her boyfriend, photographer Jack Morris (@doyoutravel) when both of them were in Fiji on a trip sponsored by the country’s tourism board. It has been a match made in influencer heaven: Travel agencies began sponsoring their trips, as well as companies such as Tiffany & Co., Walt Disney Co. , and Land Rover, and they now have about 4.7 million Instagram followers between them.

It makes sense, Ms. Karwowski said. “Influencers date other influencers or other photographers because it’s easier to get content.”

Mr. Ta hasn’t reached 1 million yet, but he is already aiming for more.

“I feel like one million these days is nothing. You need three to five [million],” he said.