<?php

namespace Illuminate\Foundation\Console;

use Illuminate\Console\Command;
use Symfony\Component\Console\Input\InputOption;

class ServeCommand extends Command
{
    /**
     * The console command name.
     *
     * @var string
     */
    protected $name = 'serve';

    /**
     * The console command description.
     *
     * @var string
     */
    protected $description = 'Serve the application on the PHP development server';

    /**
     * Execute the console command.
     *
     * @return void
     */
    public function fire()
    {
        chdir($this->laravel->publicPath());

        $host = $this->input->getOption('host');

        $port = $this->input->getOption('port');

        $base = $this->laravel->basePath();

        $this->info("Laravel development server started on http://{$host}:{$port}/");

        passthru('"'.PHP_BINARY.'"'." -S {$host}:{$port} \"{$base}\"/server.php");
    }

    /**
     * Get the console command options.
     *
     * @return array
     */
    protected function getOptions()
    {
        return [
            ['host', null, InputOption::VALUE_OPTIONAL, 'The host address to serve the application on.', 'localhost'],

            ['port', null, InputOption::VALUE_OPTIONAL, 'The port to serve the application on.', 8000],
        ];
    }
}

<?php

namespace Illuminate\Foundation\Console;

use Illuminate\Console\Command;
use Symfony\Component\Console\Input\InputOption;

class ServeCommand extends Command
{
    /**
     * The console command name.
     *
     * @var string
     */
    protected $name = 'serve';

    /**
     * The console command description.
     *
     * @var string
     */
    protected $description = 'Serve the application on the PHP development server';

    /**
     * Execute the console command.
     *
     * @return void
     */
    public function fire()
    {
        chdir($this->laravel->publicPath());

        $host = $this->input->getOption('host');

        $port = $this->input->getOption('port');

        $base = $this->laravel->basePath();

        $this->info("Laravel development server started on http://{$host}:{$port}/");
        
        if (defined('HHVM_VERSION') && HHVM_VERSION >= '3.8.0') {
            passthru('"'.PHP_BINARY.'"'." -m server -v Server.Type=proxygen -v Server.SourceRoot=\"{$base}\"/ -v Server.IP={$host} -v Server.Port={$port} -v Server.DefaultDocument=server.php -v Server.ErrorDocument404=server.php");
        } else {
            passthru('"'.PHP_BINARY.'"'." -S {$host}:{$port} \"{$base}\"/server.php");
        }
    }

    /**
     * Get the console command options.
     *
     * @return array
     */
    protected function getOptions()
    {
        return [
            ['host', null, InputOption::VALUE_OPTIONAL, 'The host address to serve the application on.', 'localhost'],

            ['port', null, InputOption::VALUE_OPTIONAL, 'The port to serve the application on.', 8000],
        ];
    }
}

Add HHVM >= 3.8.0 support in the artisan serve command via Proxygen Web Server
Add HHVM >= 3.8.0 support in the artisan serve command via Proxygen Web Server

Now we can run Laravel development server with HHVM, like this:
hhvm artisan serve